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 A320501 #3 Oct 22 2018 20:55:16 %S A320501 1,4,11,110,1804,46416,2393422,208975042,32411910059 %N A320501 Main diagonal of array in A320500. %Y A320501 Cf. A320500. %K A320501 nonn,more %O A320501 1,2 %A A320501 _N. J. A. Sloane_, Oct 22 2018, based on email from _Don Knuth_, Oct 20 2018