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 A051915 Numbers k such that 2*k! + 1 is prime. 12
 0, 1, 2, 3, 5, 12, 18, 35, 51, 53, 78, 209, 396, 4166, 9091, 9587, 13357, 15917, 17652, 46127 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS Used PrimeForm to prove primality for n = 4166 (classical N-1 test). - David Radcliffe, May 28 2007 LINKS Table of n, a(n) for n=1..20. EXAMPLE k = 5 is here because 2*5! + 1 = 241 is prime. MATHEMATICA Select[Range[0, 400], PrimeQ[2*#! + 1] &] (* Vladimir Joseph Stephan Orlovsky, Feb 13 2012 *) PROG (Magma) [n: n in [0..1000] | IsPrime(2*Factorial(n) +1)]; // Vincenzo Librandi, Feb 21 2015 (PARI) is(k) = ispseudoprime(2*k!+1); \\ Jinyuan Wang, Feb 05 2020 CROSSREFS Cf. A002981, A076679, A076680, A076681, A076682, A076683, A178488, A180626, A126896. Sequence in context: A140489 A331101 A193776 * A064688 A089891 A282237 Adjacent sequences: A051912 A051913 A051914 * A051916 A051917 A051918 KEYWORD nonn,more AUTHOR Labos Elemer, Dec 18 1999 EXTENSIONS 4166 from David Radcliffe, May 28 2007 More terms from Serge Batalov, Feb 18 2015 STATUS approved

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Last modified November 28 22:05 EST 2023. Contains 367422 sequences. (Running on oeis4.)