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ERDőS #779 · PARTIAL

Erdős problem #779 — wave 6l

Access date: 2026-07-27 UTC

Outcome

The problem is not solved here. I obtained:

1. an elementary exact decomposition of the problem into a Cramér-scale

prime-gap term and a residual prescribed-gap prime-pair term;

2. a network-free verifier which reconstructs the primorials and uses PARI/GP

APRCL to certify explicit witnesses for every \(2\leq n\leq100\);

3. an exhaustive check of the short-interval bijection for \(2\leq n\leq15\);

4. a separately labelled BPSW (probable-prime, not proof) witness check at

\(n=3001\), just beyond the first 3000 cases reported in the strongest

primary source I found; and

5. measured costs explaining why extending the current table, and especially

turning the large probable primes into certified primes, is not a

few-CPU-minute task.

Claim labels used below:

No claim labelled [C] or [D] is used as a theorem.

Step 0: authoritative live-page gate

I fetched the live page and its discussion thread through the Bright Data

browser route (not direct curl):

Verbatim live statement

> Let \(n> 1\) and \(p_1<\cdots

> \(P=\prod_{1\leq i\leq n}p_i\). Does there always exist some prime \(p\)

> with \(p_n

Live status and page-supplied information

The badge is FALSIFIABLE (this is a type of open status, not

“falsified”). The page explicitly says that its open status is the current

belief of the site owner. It lists:

Thus the mandatory skip condition did not fire.

The page calls this a problem of Deaconescu, says Erdős expected the least

such \(p\) to satisfy \(p\leq n^{O(1)}\), and says Deaconescu verified the

conjecture for \(n\leq1000\). It also gives a random-prime heuristic and

links OEIS A005235.

Clicking the page's bibliography entry gives:

> [Gu83] R. Guy, A Miscellany of Erdős Problems. Amer. Math. Month.

> (1983), 118–120.

The bibliographic record exists as American Mathematical Monthly 90(2),

118–120, DOI

10.1080/00029890.1983.11971168.

The publisher did not expose the full text in this environment, so I verified

the metadata but do not claim an independent full-text check of Guy's wording.

All four live comments

The discussion thread contained the following substantive content:

1. Giorgos Kalogeropoulos, 2025-10-31: suggested the related sequence

A005235; the site notes that it was subsequently added.

2. Dogmachine, 2025-09-22: observed that the conjecture would make every

primorial a difference of two primes, that even this weaker unrestricted

claim has no known proof, and that the left-hand inequality can be omitted.

3. StijnC, 2025-09-22: compared the unrestricted difference problem with the

twin-prime problem and Schinzel's hypothesis H, while noting the difficulty.

4. Dogmachine, 2025-08-09: compared the question with Fortune's conjecture

and called it similarly intractable with current methods.

These are comments, not verified results. Section 3 below proves the

left-hand-inequality observation and spells out the uniformity missing from

the Schinzel-H observation.

1. Literature search

I searched the exact statement, “Deaconescu” plus primorial/prime, A005235,

Fortune's conjecture, the Guy citation, and recent work through July 2026.

I found no primary source claiming a proof or counterexample to #779.

This is a report of the search, not a proof that no such source exists.

1.1 Directly relevant sources

1. **Solomon W. Golomb, “The Evidence for Fortune's Conjecture,”

Mathematics Magazine 54(4) (1981), 209–210.**

DOI

10.1080/0025570X.1981.11976928.

The journal metadata and title are verified. This is the classical

source for the stronger assertion about the least offset.

2. **Antonín Čejchan, Michal Křížek, and Lawrence Somer, “On Remarkable

Properties of Primes Near Factorials and Primorials,” *Journal of Integer

Sequences* 25 (2022), Article 22.1.4.**

Primary HTML

and

PDF.

Their Theorem 17 states that, for consecutive primes \(q

\(Q\) satisfies

\[ q\# +1

then \(Q-q\#\) is prime. [A, as reproved below]

Their Remark 21 reports that Fortune's conjecture has been checked for the

first 3000 primes, via A005235. [D]

3. **Cyril Banderier, “Fortunate and unfortunate primes: nearest primes from

a prime factorial.”**

Author's computation page.

The currently served page says \(n<1300\), explicitly warns that its large

“prime” decisions used probable-prime algorithms, and records a later

independent Mathematica check through \(n=2000\). [D]

4. **Hayat Rezgui, “New explorations and remarkable inequalities related to

Fortune's conjecture and fortunate numbers,” *General Letters in

Mathematics* 13(3) (2023), 58–76.**

DOI

10.31559/glm2023.13.3.1.

The abstract and paper describe a sufficient special case and numerical

inequalities for the first 3000 entries; they do not supply the missing

uniform prime-gap or prime-pair theorem. [D for the 3000-case data]

5. **Michael M. Ross, “Sifted Symmetry and Sieve Structures of Primorial

Goldbach Complements,” Zenodo record 21194754, version dated 2026-07-23.**

Record.

This is a very recent, non-peer-reviewed preprint mainly about the

lower-side (Goldbach/lesser-Fortunate) problem. Its Remark 5.6 accurately

restates the upper-side \(p_{n+1}^2\) criterion and the 3000-case report;

it does not claim to solve the upper-side question here.

6. OEIS A005235.

Entry and

current 4600-row b-file.

This is an auxiliary live database, not a proof source. The entry text

still says “first 2000,” the 2022 JIS paper says 3000, and the current

b-file contains 4600 candidate offsets. No primality certificates for the

enormous shifted primorials accompany that b-file. [D]

1.2 General prime-gap benchmark

R. C. Baker, G. Harman, and J. Pintz, “The Difference Between Consecutive

Primes, II,” Proceedings of the London Mathematical Society 83 (2001),

532–562, DOI

10.1112/plms/83.3.532, prove that

every sufficiently large interval \([x,x+x^{0.525}]\) contains a prime.

[B: Baker–Harman–Pintz] This is vastly longer than the

\(O((\log x)^2)\) interval needed by the short-gap route below.

2. Definitions and relation to A005235

Write

\[ P=P_n=\prod_{i=1}^n p_i,\qquad r=p_{n+1}. \]

Define the least nontrivial upper offset

\[ F_n=\min\{m>1:P+m\ \hbox{is prime}\}. \]

This is A005235's Fortunate number. Fortune's conjecture says \(F_n\) is

always prime. Problem #779 is weaker in one sense—it permits any prime

offset, not necessarily the least one—but it also explicitly requires the

offset to be below \(P\).

An A005235 value is therefore a #779 witness whenever it is actually prime,

\(P+F_n\) is actually prime, and \(F_n[A]

3. Elementary exact reduction

Lemma 1: the lower inequality is automatic

If \(p\) and \(P+p\) are prime, then \(p>p_n\). [A]

Proof. If \(p\leq p_n\), then \(p\mid P\), hence

\(p\mid(P+p)\). But \(P+p>p\), so \(P+p\) would be composite. \(\square\)

Thus the “left-most inequality can be omitted” comment is correct.

Lemma 2: rough offsets and the square threshold

If \(m>1\) and \(P+m\) is prime, then every prime divisor of \(m\) is at

least \(r=p_{n+1}\). Consequently,

\[ 1[A]

Proof. If a prime \(\ell\leq p_n\) divided \(m\), then it would divide

both \(P\) and \(P+m\). Since \(P+m>P\geq\ell\), this contradicts the

primality of \(P+m\). Thus \(m\) is \(p_n\)-rough. If it were composite,

its least prime factor and its cofactor would both be at least \(r\), giving

\(m\geq r^2\). \(\square\)

Lemma 3: the square window lies inside the required range

For every \(n\geq4\),

\[ p_{n+1}^2[A]

Proof. At \(n=4\), \(11^2=121<210=P_4\). If

\(P_n>p_{n+1}^2\), let \(s=p_{n+2}\). Bertrand's postulate gives

\(s<2p_{n+1}\), while

\[ P_{n+1}=P_n p_{n+1}>p_{n+1}^3>4p_{n+1}^2>s^2. \]

This proves the induction. \(\square\)

Proposition 4: exact Cramér-window bijection

For an integer \(H\) with \(2

bijection

\[ \begin{split} \{Q:\;&P+1In particular,

\[ \#\{p[A]

Proof. Given a prime \(Q\) on the left, set \(m=Q-P\). Then

\(1

\(p\mapsto P+p\). The two maps are inverse. \(\square\)

The verifier exhaustively checks (3), with \(H=r^2\), for every

\(2\leq n\leq15\). [D]

Corollary 5: exact split of #779

For \(n\geq4\), let

\[ T_n=\#\{p:\ r^2\leq pThen the total number \(W_n\) of #779 witnesses is exactly

\[ \boxed{ W_n=\pi(P+r^2-1)-\pi(P+1)+T_n. } \tag{5} \]

Problem #779 is equivalent to \(W_n>0\) for every \(n\geq4\), together

with the direct cases \(n=2,3\). [A]

The direct cases are

\[ n=2:\ P=6,\ p=5,\ P+p=11;\qquad n=3:\ P=30,\ p=7,\ P+p=37. \]

[A]

Formula (5) isolates two genuinely different possible routes:

1. Cramér-scale route. Prove that \((P+1,P+r^2)\) contains a prime.

By (3), its offset is automatically prime and, by (2), below \(P\).

2. Tail prime-pair route. If that short interval is empty, prove

\(T_n>0\), i.e. find a prime \(p\in[r^2,P)\) for which \(p+P\) is

prime.

Neither implication is lost: (5) is an equality, not a heuristic.

4. The exact missing analytic statements

4.1 Short-gap route

A sufficient lemma is the pointwise bound

\[ \min\{m>1:P_n+m\ {\rm prime}\}Finite remaining \(n\) could then be checked. [A]

Since

\[ \log P_n=\vartheta(p_n)\sim p_n,\qquad p_{n+1}^2\sim(\log P_n)^2, \]

(6) is a Cramér-scale prime-gap assertion at the sparse points \(P_n\).

[B: prime number theorem]

Baker–Harman–Pintz only supplies an interval of length

\(P_n^{0.525}\), which is exponentially larger than

\(p_{n+1}^2=n^{2+o(1)}\). [B: Baker–Harman–Pintz and PNT]

It therefore cannot trigger Lemma 2.

4.2 Tail route and the parity barrier

The tail asks for a lower bound on

\[ R(P;P)=\sum_{\substack{pfor the prescribed, growing even shift \(P=P_n\). A uniform

Hardy–Littlewood prime-pair asymptotic valid pointwise when the shift and

search length are both \(P\) would give

\[ R(P;P)\sim 2C_2\!\!\prod_{\substack{\ell\mid P\\\ell>2}} \frac{\ell-1}{\ell-2} \int_2^P\frac{dt}{\log t\,\log(t+P)}. \tag{8} \]

For a primorial,

\[ 2C_2\prod_{3\leq\ell\leq p_n}\frac{\ell-1}{\ell-2} \sim e^\gamma\log p_n, \]

so (8) predicts

\[ R(P;P)\sim e^\gamma\log p_n\,\frac{P}{(\log P)^2}\longrightarrow\infty. \tag{9} \]

[C: Hardy–Littlewood heuristic; not a theorem]

The exact missing lemma on this route is a positive pointwise lower bound

for (7), uniformly at \(h=x=P_n\). Ordinary two-dimensional sieve gives

upper bounds but not a positive lower bound for two simultaneous primes:

this is the parity obstruction.

Qualitative Schinzel H applied after fixing a single \(P\) predicts

infinitely many primes \(p,p+P\), but it gives no uniform guarantee that

one occurs before \(p=P\). Thus the qualitative fixed-polynomial statement

does not, by itself, prove the upper bound required in #779. **[A: logical

quantifier observation]**

Likewise, bounded-gap theorems locate some recurring bounded gap; they do

not force the specified growing gap \(P_n\). [A]

5. Reproducible computation

The standalone verifier is:

runs/erdos779_wave6l_verify.py

It uses only the Python standard library and the installed PARI/GP

executable. It does not download or trust the OEIS table at runtime:

candidate offsets are embedded, the first 4602 primes are rebuilt with an

Eratosthenes sieve, and every asserted arithmetic relation is recomputed.

Run:

python runs/erdos779_wave6l_verify.py

PARI/GP version in the successful run: 2.15.4.

5.1 Exact finite block \(2\leq n\leq100\)

For all 99 values \(2\leq n\leq100\), the verifier checks:

  • the offset \(p\) is prime;
  • \(p_n
  • isprime(P_n+p,2) == 1.

PARI documents flag 2 as the deterministic APRCL primality test, not BPSW.

No external certificate file is emitted, so I conservatively classify this

finite block as [D] computational-only, albeit with a proof-grade

primality algorithm rather than a probable-prime test.

Selected rows:

| \(n\) | \(p_n\) | witness \(p\) | digits of \(P_n\) | result |

|---:|---:|---:|---:|:---|

| 2 | 3 | 5 | 1 | APRCL prime \(P+p=11\) |

| 3 | 5 | 7 | 2 | APRCL prime \(P+p=37\) |

| 4 | 7 | 13 | 3 | APRCL prime \(P+p=223\) |

| 5 | 11 | 23 | 4 | APRCL prime \(P+p=2333\) |

| 10 | 29 | 61 | 10 | APRCL prime |

| 25 | 97 | 103 | 37 | APRCL prime |

| 50 | 229 | 293 | 92 | APRCL prime |

| 75 | 379 | 409 | 154 | APRCL prime |

| 100 | 541 | 641 | 220 | APRCL prime |

The complete 99-row transcript is deterministically represented by

small_table_sha256 =
a2bfc46bfeea17cb9f9b674167f506261dcd019fe8244250db1f2746e87a164d

The largest offset in this block is \(1381\), at \(n=70\), and all full

integer rows are generated by the verifier. [D]

5.2 Exhaustive short-window identity

For each \(2\leq n\leq15\), the script enumerates both sides of (3) for

\(H=p_{n+1}^2\). All tested integers are below \(2^{64}\); it uses the

standard deterministic seven-base Miller–Rabin theorem for this range.

The two sets agree in every case. **[D, rigorous modulo the deterministic

64-bit Miller–Rabin base theorem]**

The counts are

[(2, 6), (3, 10), (4, 19), (5, 23), (6, 29), (7, 25),
 (8, 38), (9, 42), (10, 35), (11, 56), (12, 54),
 (13, 45), (14, 60), (15, 67)]

and the enumerated-set transcript hash is

251e0911a815011d7bbd920ff11211e975bdbf5515c5675f07990a151f1378ee

This computation tests the implementation; Proposition 4 itself was proved

for all \(n\) independently of the computation.

5.3 A deliberately non-rigorous checkpoint at \(n=3001\)

The current A005235 b-file gives the candidate offset \(p=33211\).

The verifier independently recomputes:

n             = 3001
p_n           = 27457
digits(P_n)   = 11833
p             = 33211
isprime(p,2)  = 1
p_n < p < P_n
ispseudoprime(P_n+p) = 1   # PARI BPSW
P_n mod 1000000007 = 149874951

The exact integer \(P_n+p\), represented without printing all 11833 digits,

has

sha256(decimal(P_n+p)) =
79f309b87fca624b205ea1090716f8ccd3502fc61e4e95e384c225f04b31e777
first 32 digits = 51602038179433115646345337470223
last  32 digits = 18921544259369476798319951327881

This is [D] computational-only. BPSW passing does not prove that

\(P_{3001}+33211\) is prime, and I do not call it prime in this report.

Nor did I re-establish that 33211 is the least offset; minimality is

irrelevant for its use as a #779 candidate.

The final complete verifier run took 49.66 wall-seconds. It also

reproduced the \(n=1001\) BPSW checkpoint from Section 6.1 and the

\(n=4601\) size and heuristic inputs from Section 6.2.

5.4 Core verification code

The full executable code is in the standalone file. Its decisive PARI

calls are:

# Exact finite block:
for n in range(2, 101):
    assert p_n < witness[n] < P_n
    assert isprime(witness[n], 2)       # APRCL
    assert isprime(P_n + witness[n], 2) # APRCL

# Large checkpoint, intentionally not promoted to a proof:
assert ispseudoprime(P_1001 + 8831)     # BPSW only
assert ispseudoprime(P_3001 + 33211)    # BPSW only

The actual file constructs the primes and primorials from scratch, invokes

GP in one checked subprocess, parses all 99 certificates, performs the

independent 64-bit bijection enumeration, and hashes the transcripts.

6. Bounded failed computations and realistic cost

6.1 Proof attempt at \(n=1001\)

For the candidate \(p=8831\), \(P_{1001}+8831\) has 3397 decimal digits.

A BPSW check took about one second, but this is not a proof. PARI APRCL

required repeatedly expanding its stack; the final bounded attempt used

93.17 CPU-seconds and reached about 4.8 GB resident memory before I

interrupted it at an 8 GB configured stack. Pocklington–Lehmer mode also

failed to finish within two CPU-minutes. No exact primality claim is made.

6.2 Attempt to extend the b-file to \(n=4601\)

Here

p_4601        = 44203
digits(P_4601)= 19113

PARI nextprime(P+2) (which searches for a BPSW pseudoprime, not a proven

prime) was stopped at the hard cap of 239.94 CPU-seconds without returning

a candidate. Therefore no \(n=4601\) value is claimed.

A separate timing probe of the first prime offset \(p=44207\) found

\(P_{4601}+44207\) BPSW-composite in 22.62 seconds (PARI reported

22,620 ms). This can be repeated with

--skip-large --benchmark-4601. [D]

Under the prime-pair heuristic, a prime offset has conditional success

probability about

\[ \frac{e^\gamma\log p_{4601}}{\log P_{4601}} =0.0004329\ldots, \]

or roughly 2310 expensive survivors per success. [C] At the measured

22.7 seconds per composite test, a straightforward serial extension is

therefore approximately 15–30 core-hours, allowing for the slower successful

BPSW test and search overhead. [C: cost estimate] At a representative

\$0.05–\$0.15 per vCPU-hour, that is roughly \$1–\$5; parallel execution

would reduce wall time but not core-hours. This is why I did not run it on

the present few-minute budget.

A proof-grade ECPP certificate for an 11,833- or 19,113-digit general-form

candidate is a much larger job than the BPSW search. Extrapolating published

general-purpose ECPP/APRCL timings gives at least hundreds, plausibly

thousands, of core-hours, with substantial input-to-input variance.

[C: engineering estimate, not a theorem]

7. What has and has not been established

  • The lower inequality \(p_n[A]
  • Every prime value \(P+m\) with \(1

offset \(m\). [A]

  • Equation (5) is an exact reduction: the remaining alternatives are a

Cramér-scale gap at the primorial or a positive prescribed-gap prime-pair

count in the tail. [A]

  • Explicit #779 witnesses for \(2\leq n\leq100\) were independently

rechecked with APRCL. [D]

  • The literature reports computational verification of the stronger

Fortune conjecture through \(n=3000\), and the live OEIS b-file currently

has 4600 candidate rows. [D]

  • The \(n=3001\) shifted primorial passed BPSW in this run, but has not been

proved prime here. [D]

  • Neither the required uniform Cramér-scale prime-gap lemma nor the required

pointwise lower-bound prime-pair lemma is presently available. Hence

there is no uniformity/finiteness step closing #779.

PARTIAL: proved the exact Cramér-window/tail decomposition, APRCL-reverified witnesses for 2<=n<=100, and BPSW-checked (not proved) the n=3001 candidate; the uniform prime-gap/prime-pair step remains open.

This is the AI working report, labelled by outcome — not an independently verified claim unless marked PROVED. ← ledger