A288158 a(n) = smallest k such that k*n*2^n-1 is prime.

2, 1, 1, 2, 3, 1, 3, 3, 5, 2, 9, 5, 7, 4, 3, 14, 8, 4, 4, 9, 11, 8, 3, 7, 9, 10, 2, 36, 3, 1, 4, 6, 4, 2, 17, 3, 7, 4, 6, 14, 17, 14, 51, 3, 9, 12, 38, 8, 13, 36, 64, 30, 14, 14, 4, 19, 13, 41, 5, 19, 4, 60, 8, 20, 3, 13, 24, 10, 31, 15, 14, 42, 19, 13, 1, 30, 11, 11

Offset: 1

Author

Pierre CAMI, Jun 06 2017

Keywords

• nonn

Comments

If k = 1 then n*2^n-1 is a Woodall prime (A050918).

Links

• Pierre CAMI, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A050918.

Programs

Mathematica

Table[k = 1; While[! PrimeQ[k n*2^n - 1], k++]; k, {n, 78}] (* Michael De Vlieger, Jun 07 2017 *)

PARI

a(n) = my(k=1); while(1, if(ispseudoprime(k*n*2^n-1), return(k)); k++) \\ Felix Fröhlich, Jun 06 2017