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%I #26 Jul 04 2021 07:53:10
%S 2,1607,1873,10957
%N Numbers k such that 19^k - 18^k is prime.
%C PrimePi[ a(n) ] = {2, 253, 287, 1331, ...}. - _Alexander Adamchuk_, Feb 16 2007
%C a(5) > 10^5. - _Robert Price_, Jun 05 2012
%C Terms greater than 1000 may correspond to (unproven) strong pseudoprimes. - _M. F. Hasler_, Sep 16 2013
%o (PARI) is(n)=ispseudoprime(19^n-18^n) \\ _Charles R Greathouse IV_, Feb 20 2017
%Y Cf. A000043, A057468, A059801, A059802, A062572-A062583, A188051, A062586-A062666.
%K nonn,hard
%O 1,1
%A _Mike Oakes_, May 18 2001, May 19 2001
%E 10957 (found by _Mike Oakes_ in 2003) from _Alexander Adamchuk_, Feb 16 2007