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Numbers k such that 73^k - 72^k is prime.
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%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)