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%I #33 Sep 08 2022 08:44:59
%S 0,1,2,3,5,12,18,35,51,53,78,209,396,4166,9091,9587,13357,15917,17652,
%T 46127
%N Numbers k such that 2*k! + 1 is prime.
%C Used PrimeForm to prove primality for n = 4166 (classical N-1 test). - _David Radcliffe_, May 28 2007
%e k = 5 is here because 2*5! + 1 = 241 is prime.
%t Select[Range[0, 400], PrimeQ[2*#! + 1] &] (* _Vladimir Joseph Stephan Orlovsky_, Feb 13 2012 *)
%o (Magma) [n: n in [0..1000] | IsPrime(2*Factorial(n) +1)]; // _Vincenzo Librandi_, Feb 21 2015
%o (PARI) is(k) = ispseudoprime(2*k!+1); \\ _Jinyuan Wang_, Feb 05 2020
%Y Cf. A002981, A076679, A076680, A076681, A076682, A076683, A178488, A180626, A126896.
%K nonn,more
%O 1,3
%A _Labos Elemer_, Dec 18 1999
%E 4166 from _David Radcliffe_, May 28 2007
%E More terms from _Serge Batalov_, Feb 18 2015
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