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 A113321 #7 Apr 04 2015 21:49:03 %S A113321 1,2,4,3,6,5,9,7,12,8,14,10,17,11,19,13,22,15,25,16,27,18,30,20,33,21, %T A113321 35,23,38,24,40,26,43,28,46,29,48,31,51,32,53,34,56,36,59,37,61,39,64, %U A113321 41,67,42,69,44,72,45,74,47,77,49,80,50,82,52,85,54,88,55,90,57,93,58 %N A113321 Lexicographically earliest permutation of the natural numbers such that all positive differences between succeeding terms occur exactly once. %C A113321 inverse: A113324; A113323 = a(a(n)); %C A113321 A113322(n) = a(n+1) - a(n). %H A113321 <a href="/index/Per#IntegerPermutation">Index entries for sequences that are permutations of the natural numbers</a> %K A113321 nonn %O A113321 1,2 %A A113321 _Reinhard Zumkeller_, Oct 26 2005