This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A225397 #9 Jun 13 2017 10:31:43
%S A225397 31,109,373,409,619,823,1531,6637,70687
%N A225397 Numbers n such that (16^n + 5^n)/21 is prime.
%C A225397 All terms are primes.
%C A225397 a(10) > 10^5.
%t A225397 k=16; Do[p=Prime[n]; f=(k^p+5^p)/(k+5); If[ PrimeQ[f], Print[p] ], {n, 1, 9592}]
%o A225397 (PARI) is(n)=ispseudoprime((16^n+5^n)/21) \\ _Charles R Greathouse IV_, Jun 13 2017
%Y A225397 Cf. A128340, A128341, A128342, A128343, A227046, A128073.
%K A225397 hard,more,nonn
%O A225397 1,1
%A A225397 _Robert Price_, Jul 25 2013