A126856 Numbers n such that (31^n + 1)/32 is prime.

109, 461, 1061, 50777

Offset: 1

Author

Alexander Adamchuk, Mar 23 2007

Keywords

• bref
• hard
• more
• nonn

Comments

All terms are primes.

a(5) > 10^5. - Robert Price, Jul 12 2013

Links

• J. Brillhart et al., Factorizations of b^n +- 1, Contemporary Mathematics, Vol. 22, Amer. Math. Soc., Providence, RI, 3rd edition, 2002.
• H. Dubner and T. Granlund, Primes of the Form (b^n+1)/(b+1), J. Integer Sequences, 3 (2000), #P00.2.7.
• Eric Weisstein's World of Mathematics, Repunit.
• H. Lifchitz, Mersenne and Fermat primes field

Crossrefs

Cf. A000978 = numbers n such that (2^n + 1)/3 is prime. Cf. A007658, A057171, A057172, A057173, A057175, A001562, A057177, A057178, A057179, A057180, A057181, A057182, A057183, A057184, A057185, A057186, A057187, A057188, A057189, A057190, A057191, A071380, A071381, A071382. Cf. A084741, A084742, A065507, A126659.

Programs

Mathematica

Do[ p=Prime[n]; If[ PrimeQ[ (31^p + 1)/32 ], Print[p] ], {n,1,1100} ]

PARI

is(n)=isprime((31^n+1)/32) \\ Charles R Greathouse IV, Feb 17 2017

Extensions

a(4) from Robert Price, Jul 12 2013