A062587 Numbers k such that 21^k - 20^k is prime.

2, 19, 41, 43, 337, 479, 9127, 37549, 44017, 59971, 128327, 176191, 193601

Offset

1,1

Comments

Terms greater than 1000 may correspond to (unproven) strong pseudoprimes.

Links

Table of n, a(n) for n=1..13.

Top probable primes of the form 21^p-20^p

Prog

(PARI) is(n)=ispseudoprime(21^n-20^n) \\ Charles R Greathouse IV, Jun 13 2017

Crossrefs

Cf. A000043, A057468, A059801, A059802, A062572-A062666.

Sequence in context: A107143 A018610 A075682 * A109946 A141067 A296251

Adjacent sequences: A062584 A062585 A062586 * A062588 A062589 A062590

Keyword

nonn,hard

Author

Mike Oakes, May 18 2001, May 19 2001

Extensions

a(8) from Jean-Louis Charton, Feb 29 2012

a(9) and a(10) from Robert Price, May 30 2012

Edited by M. F. Hasler, Sep 16 2013

a(11) added by Jean-Louis Charton, Nov 24 2014

a(12) added by Jean-Louis Charton, Feb 05 2015

a(13) added by Jean-Louis Charton, Feb 18 2015

Status

approved