A056802 Numbers k such that 2*9^k + 1 is prime.

0, 1, 2, 3, 8, 15, 27, 30, 66, 90, 160, 348, 391, 411, 626, 727, 2740, 3921, 6048, 6891, 8860, 21978, 32411, 41390, 52553, 82948, 95907, 264840, 537363, 543056, 587616, 638931, 673271, 1561518

Offset: 1

Author

Robert G. Wilson v, Aug 22 2000

Keywords

• nonn
• hard
• more
• changed

Crossrefs

Cf. A003306 (k such that 2*3^k + 1 is prime).

Programs

Mathematica

Do[ If[ PrimeQ[ 2*9^n + 1], Print[ n ]], {n, 0, 1000}]

PARI

is(n)=ispseudoprime(2*9^n+1) \\ Charles R Greathouse IV, Jun 12 2017

Extensions

More terms from Rick L. Shepherd, Apr 22 2003

a(21)-a(31) from David Broadhurst, Feb 22 2010

a(32)-a(34) from Paul S. Vanderveen, Feb 09 2020