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 A217468 Composite values of n such that 2^n == 2 (mod n*(n-1)). 6
 91625794219, 8796093022207, 1557609722332488343, 18216643597893471403 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS No other terms below 2^64. The next term is <= 25790417485109157029391019 = A019320(258). - Emmanuel Vantieghem, Dec 01 2014 Terms A019320(k) belongs to this sequence for k in A297412. - Max Alekseyev, Dec 29 2017 LINKS Mersenne Forum, Prime Conjecture EXAMPLE a(1) = 91625794219 = (2^38 - 2^19 + 1)/3 = A019320(114). a(2) = 8796093022207 = 2^43 - 1 = A019320(43). PROG (PARI) is_A217468(n)={Mod(2, (n-1)*n)^n==2 & !isprime(n)}  \\ - M. F. Hasler, Oct 07 2012 CROSSREFS Cf. A069051, A216822, A219037, A217465. Intersection of A001567 and { 2*A014945(k) + 1 }. Sequence in context: A153433 A234386 A015417 * A234052 A104831 A231235 Adjacent sequences:  A217465 A217466 A217467 * A217469 A217470 A217471 KEYWORD nonn,hard,more AUTHOR V. Raman, Oct 04 2012 STATUS approved

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Last modified August 11 11:29 EDT 2022. Contains 356065 sequences. (Running on oeis4.)