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Numbers k such that 17^k + 4 is prime.
0

%I #23 Mar 22 2023 21:57:12

%S 0,2,6,18,7238

%N Numbers k such that 17^k + 4 is prime.

%C No further terms up to 10000.

%C No further terms up to 37200. - _Michael S. Branicky_, Mar 22 2023

%e For k = 0: 17^0 + 4 = 5, which is prime, so 0 is a term of the sequence.

%e For k = 2: 17^2 + 4 = 293, which is prime, so 2 is a term of the sequence.

%t Select[Range@10^5, PrimeQ[17^# + 4] &] (* _Michael De Vlieger_, Jan 03 2015 *)

%o (PARI) for(n=0, 1e5, if(ispseudoprime(17^n+4), print1(n, ", ")))

%Y Corresponding sequences for k^n+4: A058958 (k=3), A124621 (k=5), A096305(k=7), A217384 (k=9), A137236 (k=13), A247166 (k=15), A243397 (k=19).

%K nonn,more

%O 1,2

%A _Felix Fröhlich_, Dec 31 2014