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 A138727 #2 Mar 30 2012 17:33:54 %S A138727 26,42,59,75,91,107,123,139,139,139,27,43,58,74,90,106,122,138 %N A138727 Numbers n whose hexadecimal representation is the n-th member of the alphanumeric sequence: 1A, 2A, 3B, 4B, 5B, 6B, 7B, 8B, 8B, 8B, 1B, 2B, 3A, 4A, 5A, 6A, 7A, 8A. (A notation convention of the groups in the periodic table of the elements with 18 columns). %C A138727 See the periodic table of the elements with 18 columns in A138723 and A138724. See A138718 for more information. %Y A138727 Cf. A138718, A138723, A138724. %K A138727 easy,fini,full,nonn %O A138727 1,1 %A A138727 _Omar E. Pol_, Apr 16 2008