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%I #18 Jul 04 2021 09:00:41
%S 2,19,769,773,4507,26183
%N Numbers k such that 57^k - 56^k is prime.
%C Terms greater than 1000 often correspond only to strong pseudoprimes. [Clarified by _M. F. Hasler_, Sep 15 2013]
%C a(7) > 10^5. - _Robert Price_, Dec 06 2012
%o (PARI) is(n)=ispseudoprime(57^n-56^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(6) from _Robert Price_, Dec 06 2012
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