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Erdős problem #366

Are there any $2$-full $n$ such that $n+1$ is $3$-full? That is, if $p\mid n$ then $p^2\mid n$ and if $p\mid n+1$ then $p^3\mid n+1$.

Why this problem

Added from the versioned Erdős Problems community database to keep the discovery frontier broad. The first pass must validate the exact statement, status, literature, and a concrete verification contract.

Verification contract

Official database status is verifiable; refine the exact certificate contract before any candidate claim.

Tracking
Difficulty
5/10
Attempts
1
Last attempt
2026-07-20 23:11 UTC
Source status
verifiable
External validation
none
Techniques and harnesses
number theory
Resumable campaign memory

Research map

1 epochs · 0 promising · 0 blocked · 3 ruled out
Next session checkpoint

Test the single-prime-support successor branch for structural information.

First action: Write the exact factor/gcd decomposition of p^e-1 for n+1=p^e, then enumerate e>=3 and p^e<=10^6 as a regression fixture against tools/erdos366_discriminator.py.

Stop or redirect when: Stop immediately on a verified witness; otherwise stop after the declared shell and retain the route only if it proves a local obstruction or material pruning rule.

Open leads
  • Analyze n+1=p^e using the factorization of p^e-1.
    Derive gcd conditions, implement a bounded certified shell, and compare with all single-prime-support cases through 10^6.
  • Reconstruct the A060355 computation below 10^22.
    Audit OEIS history and Donovan Johnson table provenance for code and completeness arguments.
  • Formalize a future explicit witness in Lean.
    After a witness exists, instantiate the existential and compile with no sorry or admit.
Strategy registry
  • isolated adversarial reconstruction
    Recover or independently rebuild the A060355 enumeration and verify both its coverage and every listed factorization without using the present sparse target code.
  • symbolic and congruence family discovery
    Decompose p^e-1 into cyclotomic factors, exploit their controlled gcds, and test whether the powerfulness requirement forces forbidden exponent-one prime divisors.
  • counterexample and witness search
    Generate every 3-full m in the bounded domain exactly once from increasing prime supports and exponents at least three, factor m-1 exactly, and independently compare the generated set with a dense sieve oracle.
    Reopen only if: Resume undifferentiated bound extension only with a recognized target bound, an explicit request, a completeness-certificate objective, or a new structural pruning result.
Ruled out, with scope
  • Treat OEIS A060355 alone as a certified target exclusion through 10^22.
    It is a superset table and lacks an independently checked completeness certificate for the reported range.
    Reopen only if: Recover or reproduce the enumeration with a complete generator and independent certificate.
  • Routine extension of the same arbitrary search cutoff as a contribution.
    A finite null search cannot settle universal nonexistence and would not improve a verified best-known result.
    Reopen only if: A predeclared recognized bound, explicit expert request, or new structural pruning theorem.
  • Use (8,9), (12167,12168), or generic Pell-generated powerful pairs as target evidence without checking orientation and exponent three.
    They prove 3-full then 2-full, or only 2-full then 2-full.
    Reopen only if: Produce a family member whose first number independently passes 2-full and whose successor passes 3-full.
Complete history

Attempts on this problem

2026-07-20 23:11 UTCOpen-problem program · 42 min

Erdős problem #366

Mandatory source/status baseline followed by a bounded counterexample search that enumerates 3-full m=n+1, with a separate dense smallest-prime-factor oracle and reverse-orientation controls.

What this run accomplished

The official and original statements agree on the target orientation: n is 2-full and n+1 is 3-full. The maintained source remains open. A dense oracle and sparse generator agreed on exactly 307 3-full values through 10^6, with identical canonical SHA-256 hashes and no duplicates. The sparse search then examined 1,645 3-full values through 10^8 and found no target. No universal claim or candidate solution is made.

Next: Investigate the structural branch n+1=p^e with prime p and e>=3 by deriving the exact cyclotomic factor and gcd conditions for p^e-1.