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%I #20 Sep 08 2022 08:45:07
%S 2,3,4,5,6,7,14,15,17,22,28,91,253,257,298,659,832,866,1849,2495,2716,
%T 2773,2831,3364,5264,7429,28539,32123,37868
%N Numbers k such that 2*k! - 1 is prime.
%e k = 5 is here because 2*5! - 1 = 239 is prime.
%t Select[Range[8000], PrimeQ[2 #! - 1] &] (* _Vincenzo Librandi_, Feb 20 2015 *)
%o (Magma) [n: n in [1..600] | IsPrime(2*Factorial(n)-1)]; // _Vincenzo Librandi_, Feb 20 2015
%o (PARI) is(k) = ispseudoprime(2*k!-1); \\ _Jinyuan Wang_, Feb 04 2020
%Y Cf. A051915.
%Y Cf. A002982, A076134, A099350, A099351, A180627, A180628, A180629, A180630, A180631.
%K nonn,more
%O 1,1
%A Phillip L. Poplin (plpoplin(AT)bellsouth.net), Oct 30 2002
%E a(24)-a(29) from _Serge Batalov_, Feb 18 2015
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