A071381 Numbers n such that (28^n+1)/29 is a prime.

3, 19, 373, 419, 491, 1031, 83497, 223381

Offset: 1

Author

Rick L. Shepherd, May 22 2002

Keywords

• nonn
• more

Comments

(28^1031+1)/29, a 1491-digit number, has now been certified prime with Primo.

a(8) > 10^5. - Robert Price, Jul 10 2013

Links

• H. Dubner and T. Granlund, Primes of the Form (b^n+1)/(b+1), J. Integer Sequences, 3 (2000), #P00.2.7.

Crossrefs

Cf. A071380, A071382.

Programs

PARI

isok(n) = (denominator(p=(28^n+1)/29)==1) && isprime(p); \\ Michel Marcus, Oct 29 2017

Extensions

a(7) from Robert Price, Jul 10 2013

a(8)=223381 corresponds to a probable prime discovered by Paul Bourdelais, Dec 23 2020