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 A180431 #12 Feb 16 2025 08:33:13
%S A180431 0,6,522,178438
%N A180431 Numbers n such that 4*17^n+1 is prime.
%C A180431 For n>0, members of the sequence may only be of form 4k+2 (otherwise the expression is divisible by 3 or 5). Therefore members of the sequence are a subset of A005574 and are Generalized Fermat primes.
%H A180431 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/GeneralizedFermatNumber.html">Generalized Fermat Number</a>.
%e A180431 For a(2) = 6 we have 4*17^6+1 = 96550277, which is prime.
%t A180431 Do[ If[ PrimeQ[ 4*17^n+1], Print[ n ]], {n, 0, 10000}]
%o A180431 (PARI) is(n)=isprime(4*17^n+1) \\ _Charles R Greathouse IV_, May 15 2013
%Y A180431 Cf. A005574.
%K A180431 nonn,more
%O A180431 1,2
%A A180431 _Serge Batalov_, Sep 04 2010