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 A097291 #3 Mar 30 2012 18:57:05 %S A097291 1,1,2,2,1,3,3,2,3,1,4,4,2,4,3,4,1,5,5,2,5,3,5,4,5,1,6,6,2,6,3,6,4,6, %T A097291 5,6,1,7,7,2,7,3,7,4,7,5,7,6,7,1,8,8,2,8,3,8,4,8,5,8,6,8,7,8,1,9,9,2, %U A097291 9,3,9,4,9,5,9,6,9,7,9,8,9,1,10,10,2,10,3,10,4,10,5,10,6,10,7,10,8,10,9,10 %N A097291 Contains exactly once every pair (i,j) of positive integers. %C A097291 The pairs (i,j) are ordered in segments thus: segment 1: 1 segment 2: 1 2 2 segment 3: 1 3 3 2 3 segment 4: 1 4 4 2 4 3 4 segment 5: 1 5 5 2 5 3 5 4 5 and so on. %Y A097291 Cf. A098289. %K A097291 nonn %O A097291 1,3 %A A097291 _Clark Kimberling_, Aug 05 2004