%I #19 Jul 04 2021 09:02:07
%S 19,83,1091,20117
%N Numbers k such that 73^k - 72^k is prime.
%C Terms greater than 1000 are often only strong pseudoprimes.
%C a(5) > 10^5. - _Robert Price_, Apr 21 2014
%o (PARI) is(n)=ispseudoprime(73^n-72^n) \\ _Charles R Greathouse IV_, Jun 13 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(4) from _Robert Price_, Apr 21 2014 (Computer run by Adam Marciniec)