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 A120240 #2 Mar 30 2012 18:57:06 %S A120240 1,4,2,3,9,10,12,5,6,17,7,8,22,23,25,26,11,30,31,33,13,14,38,15,16,43, %T A120240 44,46,18,19,51,20,21,56,57,59,60,24,64,65,67,68,27,72,28,29,77,78,80, %U A120240 81,32,85,86,88,34,35,93,36,37,98,99,101,39,40,106,41,42,111,112,114 %N A120240 Inverse of A120239. %C A120240 A permutation of the natural numbers. %Y A120240 Cf. A120229, A120239. %K A120240 nonn %O A120240 1,2 %A A120240 _Clark Kimberling_, Jun 11 2006