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%I #20 Feb 05 2020 02:04:40
%S 0,1,2,3,4,5,9,12,17,26,76,379,438,1695,6709,13313,18504,19021,24488,
%T 45552,49085
%N Numbers k such that 3*k! - 1 is prime.
%C a(22) > 50000. - _Roger Karpin_, Nov 13 2016
%e k = 5 is here because 3*5! - 1 = 359 is prime.
%p for n from 0 to 1000 do if isprime(3*n! - 1) then print(n) end if end do;
%t Select[Range[0, 10^3], PrimeQ[3 #! - 1] &] (* _Robert Price_, May 27 2019 *)
%o (PARI) isok(n) = isprime(3*n! - 1); \\ _Michel Marcus_, Nov 13 2016
%o (PFGW) ABC2 3*$a!+1
%o a: from 1 to 1000 // _Jinyuan Wang_, Feb 04 2020
%Y Cf. A051915, A076134.
%Y Cf. A002982, A076133, A099350, A099351, A180627, A180628, A180629, A180630, A180631.
%K nonn,more
%O 1,3
%A Phillip L. Poplin (plpoplin(AT)bellsouth.net), Oct 30 2002
%E a(15)-a(21) from _Roger Karpin_, Nov 13 2016