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A076133
Numbers k such that 2*k! - 1 is prime.
11
2, 3, 4, 5, 6, 7, 14, 15, 17, 22, 28, 91, 253, 257, 298, 659, 832, 866, 1849, 2495, 2716, 2773, 2831, 3364, 5264, 7429, 28539, 32123, 37868
OFFSET
1,1
EXAMPLE
k = 5 is here because 2*5! - 1 = 239 is prime.
MATHEMATICA
Select[Range[8000], PrimeQ[2 #! - 1] &] (* Vincenzo Librandi, Feb 20 2015 *)
PROG
(Magma) [n: n in [1..600] | IsPrime(2*Factorial(n)-1)]; // Vincenzo Librandi, Feb 20 2015
(PARI) is(k) = ispseudoprime(2*k!-1); \\ Jinyuan Wang, Feb 04 2020
KEYWORD
nonn,more
AUTHOR
Phillip L. Poplin (plpoplin(AT)bellsouth.net), Oct 30 2002
EXTENSIONS
a(24)-a(29) from Serge Batalov, Feb 18 2015
STATUS
approved