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%I #24 Jul 04 2021 08:21:43
%S 2,3,5,47,67,103
%N Numbers k such that 42^k - 41^k is prime.
%C Terms greater than 1000 are often only strong pseudoprimes.
%C No further terms up to 5000. - _Harvey P. Dale_, Mar 13 2011
%C a(7) > 10^5. - _Robert Price_, Sep 21 2012
%t Select[Range[5000], PrimeQ[42^# - 41^#] &] (* _Harvey P. Dale_, Mar 13 2011 *)
%o (PARI) is(n)=ispseudoprime(42^n-41^n) \\ _Charles R Greathouse IV_, Jun 12 2017
%Y Cf. A000043, A057468, A059801, A059802, A062572-A062666.
%K nonn,hard,more
%O 1,1
%A _Mike Oakes_, May 18 2001, May 19 2001