A050880 Numbers n such that 243*2^n-1 is prime.

2, 6, 8, 11, 12, 18, 24, 27, 36, 38, 44, 56, 58, 62, 116, 134, 162, 242, 274, 348, 358, 478, 512, 548, 658, 824, 1242, 1287, 1531, 2846, 3343, 4818, 4856, 5051, 6024, 7431, 7434, 9432, 9667, 13059, 13482, 18111, 19004, 33571, 40174, 41467, 53206, 57978, 61438

Offset: 1

Author

N. J. A. Sloane, Dec 29 1999

Keywords

• hard
• nonn

Links

• Lei Zhou, Table of n, a(n) for n = 1..67
• Ray Ballinger and Wilfrid Keller, List of primes k.2^n + 1 for k < 300
• Wilfrid Keller, List of primes k.2^n - 1 for k < 300
• L. Soule and K. Bonath, Riesel Prime database
• Index entries for sequences of n such that k*2^n-1 (or k*2^n+1) is prime

Programs

Mathematica

b=3^5; i=0; Table[While[i++; cp=b*2^i-1; !PrimeQ[cp]]; i, {j, 1, 33}] (* Lei Zhou, Nov 08 2013 *)

PARI

is(n)=ispseudoprime(243*2^n-1) \\ Charles R Greathouse IV, Feb 20 2017

Extensions

More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008