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

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

Offset

1,1

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

Table of n, a(n) for n=1..8.

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

Prog

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

Crossrefs

Cf. A071380, A071382.

Sequence in context: A357956 A229832 A219270 * A195639 A195640 A195641

Adjacent sequences: A071378 A071379 A071380 * A071382 A071383 A071384

Keyword

nonn,more

Author

Rick L. Shepherd, May 22 2002

Extensions

a(7) from Robert Price, Jul 10 2013

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

Status

approved