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Numbers k such that 5*k^k + 4 is prime.
2

%I #24 Sep 02 2024 08:12:17

%S 3,5,9,183,561

%N Numbers k such that 5*k^k + 4 is prime.

%C a(6), if it exists, is greater than 5000. - _Vaclav Kotesovec_, Apr 01 2018

%C a(6), if it exists, is greater than 20000. - _Michael S. Branicky_, Sep 02 2024

%t Select[Range[1, 1000], PrimeQ[5*#^# + 4] &] (* _Vaclav Kotesovec_, Apr 01 2018 *)

%o (PARI) for(n=0, 500, if(isprime(5*n^n+4), print1(n", ")))

%o (PARI) lista(nn) = forstep(n=1, nn, 2, if(ispseudoprime(5*n^n+4), print1(n, ", "))); \\ _Altug Alkan_, Apr 01 2018

%Y Numbers k such that b*k^k + b - 1 is prime: A110932 (b=2), A160360 (b=3), A301520 (b=4), this sequence (b=5), A302090 (b=6).

%Y Cf. A302089.

%K nonn,more,hard

%O 1,1

%A _Seiichi Manyama_, Apr 01 2018

%E a(5) from _Vaclav Kotesovec_, Apr 01 2018