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A334797
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Primes q such that p-1 | q-1 or q-1 | p-1 for every prime p | 2^(q-1)-1.
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1
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2, 3, 5, 7, 11, 13, 17, 19, 23, 31, 37, 43, 47, 59, 79, 83, 107, 167, 179, 223, 227, 263, 347, 359, 367, 383, 467, 479, 503, 563, 587, 719, 839, 863, 887, 983, 1019, 1187, 1283, 1307, 1319, 1367, 1439, 1487, 1523, 1619, 1823, 1907, 2027, 2039, 2063, 2099, 2207
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OFFSET
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1,1
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COMMENTS
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Are there infinitely many such primes?
Are there only finitely many such primes that are not safe primes?
Is their set {2, 3, 13, 17, 19, 31, 37, 43, 79, 223, 367} complete?
It is assumed that there are infinitely many safe primes (and their estimated asymptotic density ~ 1.32/(log n)^2 converges to the actual value as far as we know), so the answer to the first question is certainly "yes". - M. F. Hasler, Jun 14 2021
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LINKS
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MATHEMATICA
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seqQ[q_] := PrimeQ[q] && Module[{ps = FactorInteger[2^(q - 1) - 1][[;; , 1]]}, AllTrue[ps, Divisible[# - 1, q - 1] || Divisible[q - 1, # - 1] &]]; Select[Range[100], seqQ] (* Amiram Eldar, Jun 09 2020 *)
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PROG
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(PARI) isok(q) = {if (! isprime(q), return (0)); my(f=factor(2^(q-1)-1)[, 1]~, qq=q-1); for (k=1, #f, my(pp=f[k]-1); if ((qq % pp) && (pp % qq), return(0)); ); return (1); } \\ Michel Marcus, Jun 09 2020
(PARI) is_A334797(n)={isprime(n)&&!foreach(factor(2^n---1)[, 1], p, n%(p-1)&&(p-1)%n&&return)} \\ M. F. Hasler, Jun 14 2021
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CROSSREFS
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KEYWORD
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nonn,hard
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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