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 A194904 #5 Mar 30 2012 18:57:44 %S A194904 1,3,2,5,4,6,8,10,7,9,12,14,11,13,15,17,19,21,16,18,20,23,25,27,22,24, %T A194904 26,28,30,32,34,36,29,31,33,35,38,40,42,44,37,39,41,43,45,47,49,51,53, %U A194904 55,46,48,50,52,54,57,59,61,63,65,56,58,60,62,64,66,68,70,72 %N A194904 Inverse permutation of A194903; every positive integer occurs exactly once. %t A194904 (See A194902.) %Y A194904 Cf. A194902, A194903. %K A194904 nonn %O A194904 1,2 %A A194904 _Clark Kimberling_, Sep 05 2011