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 A338412 #21 Jan 21 2022 03:44:08 %S A338412 3,6207,8076,22356,151456 %N A338412 Numbers k such that k * 20^k + 1 is prime. %C A338412 a(6) > 219976. %H A338412 Steven Harvey, <a href="http://harvey563.tripod.com/GClist.txt">Generalized Cullen Search</a> %H A338412 G. Loeh, <a href="http://guenter.loeh.name/gc/status.html">Generalized Cullen primes</a> %H A338412 Wikipedia, <a href="https://en.wikipedia.org/wiki/Cullen_number">Cullen number</a> %t A338412 Select[Range[1, 10000], PrimeQ[n*20^n+1] &] %o A338412 (PARI) for(n=1, 10000, if(isprime(n*20^n+1), print1(n, ", "))) %o A338412 (Magma) [n: n in [1..10000] |IsPrime(n*20^n+1)] %Y A338412 Numbers k such that k * b^k + 1 is prime: A006093 (b=1), A005849 (b=2), A006552 (b=3), A007646 (b=4), A242176 (b=6), A242177 (b=7), A242178 (b=8), A265013 (b=9), A007647(b=10), A242196(b=12), A242197 (b=14), A242198 (b=15), A242199 (b=16), A007648 (b=18), this sequence (b=20). %K A338412 nonn,more,hard %O A338412 1,1 %A A338412 _Tim Johannes Ohrtmann_, Oct 25 2020