When is sigma(sigma(2p - 1)) prime?
TheoremDB P11382 · number theory
Inferred from the community field; finer classification has not been reviewed.
Problem statement
Let be the sum of the positive divisors of the positive integer k. Classify all primes p for which q=sigma(sigma(2p-1)) is prime. Determine whether every such output q is a Mersenne prime, meaning q=2^r-1 for some prime r.
Lean 4
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Background
Additional formulation recorded by the source
Classify {p prime : sigma(sigma(2p-1)) is prime} and determine whether each prime output has the form 2^r-1 with r prime.
Progress & source assessment
Source-reported assessment, retrieved 8 September 2026. Frontier Science has not independently reviewed this status.
Open. No signed Lean verification is attached to this problem or its selected resolution.
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