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 A012840 #4 Feb 24 2012 12:51:10 %S A012840 1,1,1,6,21,120,765,5376,46473,415104,4371225,48143744,594635613, %T A012840 7784817664,110691178325,1673986906112,27018807872657,462531126525952, %U A012840 8370279766396593,159859054841331712 %N A012840 exp(sec(x)*arctanh(x))=1+x+1/2!*x^2+6/3!*x^3+21/4!*x^4+120/5!*x^5... %K A012840 nonn %O A012840 0,4 %A A012840 Patrick Demichel (patrick.demichel(AT)hp.com)