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%I #16 Jul 04 2021 07:53:53
%S 2,3,5,211
%N Numbers k such that 31^k - 30^k is prime.
%C Terms > 1000 are often only strong pseudoprimes.
%C a(5) > 10^5 - _Robert Price_, Nov 14 2012
%o (PARI) is(n)=ispseudoprime(31^n-30^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
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