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Numbers k such that 3*k! - 1 is prime.
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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