A306573 Numbers k such that 11^(k+7) + 7^(k+5) + 5^(k+3) + 3^(k+2) + 2^(k+1) + 1 is prime.

3, 5, 7, 81, 185, 254, 623, 1087, 2407, 7862, 8721, 9353, 13154, 63003

Offset: 1

Author

Mikk Heidemaa, Feb 24 2019

Keywords

• nonn
• more
• hard

Comments

a(14) > 41000. - Michael S. Branicky, Mar 25 2023

Programs

Mathematica

ParallelMap[If[PrimeQ[11^(#+7) + 7^(#+5) + 5^(#+3) + 3^(#+2) + 2^(#+1) + 1], #, Nothing] &, Range@8000]

PARI

is(n) = ispseudoprime(11^(n+7) + 7^(n+5) + 5^(n+3) + 3^(n+2) + 2^(n+1) + 1) \\ Felix Fröhlich, Mar 06 2019

Extensions

a(14) from Michael S. Branicky, May 15 2025