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 A337846 Odd integers k such that 2^((k-1)/2) == 1 (mod k*(k-2)). 2
 17, 257, 457, 1297, 6481, 11953, 26321, 47521, 47881, 49681, 65537, 74449, 157081, 165601, 278497, 333433, 476737, 557041, 560737, 576721, 1033057, 1266841, 1329337, 1463617, 1468897, 2291041, 2422201, 2754481, 2851633, 2969137, 3255281 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Computed terms are prime. Is this a possible primality test or are there pseudo primes? Terms are of the form 8k+1. The Fermat number F(5) = A000215(5) = 4294967297 = 641*6700417 is the smallest composite counterexample. - Hugo Pfoertner, Sep 26 2020 LINKS Table of n, a(n) for n=1..31. MATHEMATICA Select[Range[3, 10^6, 2], PowerMod[2, (# - 1)/2, #*(# - 2)] == 1 &] (* Amiram Eldar, Sep 26 2020 *) PROG (PARI) is(n) = n%2 && n>=3 && Mod(2, n*(n-2))^((n-1)/2) == 1 CROSSREFS Cf. A081762, A337818. Sequence in context: A090457 A342481 A355876 * A174408 A260072 A260407 Adjacent sequences: A337843 A337844 A337845 * A337847 A337848 A337849 KEYWORD nonn AUTHOR Benoit Cloitre, Sep 26 2020 STATUS approved

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Last modified August 7 10:36 EDT 2024. Contains 375011 sequences. (Running on oeis4.)