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%I #11 Jul 13 2023 15:22:59
%S 2,3,17,74,120,212,528,2348,13820
%N Numbers k such that k^7 + 7*k + 7^k is prime.
%t Select[Range[5000], PrimeQ[#^7 + 7*# + 7^#]&]
%o (PARI) is(n)=ispseudoprime(n^7+7*n+7^n) \\ _Charles R Greathouse IV_, Jun 13 2017
%Y Cf. A220528.
%K nonn,more
%O 1,1
%A _Vincenzo Librandi_, Jan 07 2013
%E a(9) from _Michael S. Branicky_, Jul 13 2023
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