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 A117137 #4 Mar 30 2012 16:50:24 %S A117137 1,1,2,4,1,3,6,2,7,1,4,8,3,9,2,10,1,5,10,4,11,3,12,2,13,1,6,12,5,13,4, %T A117137 14,3,15,2,16,1,7,14,6,15,5,16,4,17,3,18,2,19,1 %N A117137 Same as triangle in A117136, but omit final 1 from each row. %C A117137 Row n has length 2n+1. %e A117137 Triangle begins: %e A117137 Row 0: 1 %e A117137 Row 1: 1 2 4 %e A117137 Row 2: 1 3 6 2 7 %e A117137 Row 3: 1 4 8 3 9 2 10 %e A117137 Row 4: 1 5 10 4 11 3 12 2 13 %e A117137 ... %Y A117137 Cf. A117136, A046901, A008344. %Y A117137 The segments of A046901 appear as rows 2, 7, 22, 67, ... (A060816) of this array. %K A117137 nonn,tabf %O A117137 0,3 %A A117137 _N. J. A. Sloane_, Apr 21 2006