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A180628
Numbers k such that 7*k! - 1 is prime.
8
2, 3, 4, 5, 6, 7, 8, 12, 23, 25, 31, 57, 74, 86, 140, 240, 310, 703, 713, 796, 1028, 1102, 1924, 3469, 3990
OFFSET
1,1
COMMENTS
a(26) > 12000. - Michael S. Branicky, Jul 07 2024
MATHEMATICA
fQ[n_] := PrimeQ[7 n! - 1]; k = 0; lst = {}; While[k < 1501, If[ fQ@k, AppendTo[lst, k]; Print@k]; k++ ]; lst
Select[Range[4000], PrimeQ[7#!-1]&] (* Harvey P. Dale, Apr 22 2024 *)
PROG
(PARI) is(k) = ispseudoprime(7*k!-1); \\ Jinyuan Wang, Feb 03 2020
KEYWORD
nonn,more
AUTHOR
Robert G. Wilson v, Sep 13 2010
EXTENSIONS
a(23) from Jinyuan Wang, Feb 03 2020
a(24)-a(25) from Michael S. Branicky, Apr 25 2023
STATUS
approved