A057187 Numbers n such that (21^n+1)/22 is a prime.

3, 5, 7, 13, 37, 347, 17597, 59183, 80761, 210599, 394579

Offset

1,1

Comments

Some of the larger terms correspond to probable primes.

Links

Table of n, a(n) for n=1..11.

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

H. Lifchitz, Mersenne and Fermat primes field

Paul Bourdelais, A Generalized Repunit Conjecture [From Paul Bourdelais, Mar 24 2010]

Prog

(Prime95) PRP=1, 21, 394579, 1, 0, 0, "22"

Crossrefs

Sequence in context: A369433 A075557 A244452 * A163080 A141414 A236464

Adjacent sequences: A057184 A057185 A057186 * A057188 A057189 A057190

Keyword

nonn

Author

N. J. A. Sloane, Sep 15 2000

Extensions

a(7) from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 05 2008

a(8) corresponds to a probable prime discovered by Paul Bourdelais, Mar 22 2010

a(9) corresponds to a probable prime discovered by Paul Bourdelais, Mar 24 2010

a(10) corresponds to a probable prime discovered by Paul Bourdelais, Aug 30 2013

a(11) corresponds to a probable prime discovered by Paul Bourdelais, Oct 23 2018

Status

approved