A236169 Numbers n such that n!*3^n + 1 is prime.

0, 2, 3, 8, 13, 19, 124, 199, 288, 359, 692, 3610, 5316, 5372, 7442, 8251, 14288, 16883, 17131

Offset: 1

Author

Robert Price, Jan 19 2014

Keywords

• nonn
• more

Comments

a(20) > 25000.

Corresponding primes are all verified prime (i.e., not probable prime): 2, 19, 163, 264539521, 9927882482918401, 141383412854531380076544001, ...

Crossrefs

Cf. A091415, A002982, A121859.

Programs

Mathematica

Do[f=n!*3^n+1;If[PrimeQ[f],Print[{n,f}]],{n,0,25000}]

PARI

isok(n) = isprime(n!*3^n + 1); \\ Michel Marcus, Jul 23 2017

Extensions

a(1)=0 prepended by Robert Price, Jul 22 2017