A062586 - OEIS

%I #20 Jul 04 2021 08:43:16

%S 5,17,109,1979,6899,7331,18661,79621,81649

%N Numbers k such that 20^k - 19^k is prime.

%C Terms k > 1000 may correspond to (unproven) strong pseudoprimes.

%H Henri Lifchitz and Renaud Lifchitz, <a href="http://www.primenumbers.net/prptop/searchform.php?form=20%5Ep-19%5Ep">Top probable primes of the form 20^p-19^p</a>

%o (PARI) is(n)=ispseudoprime(20^n-19^n) \\ _Charles R Greathouse IV_, Jun 12 2017

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

%K nonn,hard

%O 1,1

%A _Mike Oakes_, May 18 2001, May 19 2001

%E a(7)-a(9) found by _Jean-Louis Charton_ in February and March 2011

%E Edited by _M. F. Hasler_, Sep 16 2013