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 A143956 #4 Apr 05 2012 18:14:47 %S A143956 1,3,2,5,4,2,7,6,4,2,9,8,6,4,2,11,10,8,6,4,2,13,12,10,8,6,4,2,15,14, %T A143956 12,10,8,6,4,2,17,16,14,12,10,8,6,4,2,19,18,16,14,12,10,8,6,4,2,21,20, %U A143956 18,16,14,12,10,8,6,4,2 %N A143956 Triangle read by rows, A000012 * A136521 * A000012; 1<=k<=n. %C A143956 Row sums = A028387: (1, 5, 11, 19, 29, 41,...) %F A143956 Triangle read by rows, A000012 * A136521 * A000012; 1<=k<=n. A136521 = an infinite lower triangular matrix with (1,2,2,2,...) in the main diagonal the rest zeros. %e A143956 First few rows of the triangle = %e A143956 1; %e A143956 3, 2; %e A143956 5, 4, 2; %e A143956 7, 6, 4, 2; %e A143956 9, 8, 6, 4, 2; %e A143956 11, 10, 8, 6, 4, 2; %e A143956 13, 12, 10, 8, 6, 4, 2; %e A143956 15, 14, 12, 10, 8, 6, 4, 2; %e A143956 ... %Y A143956 Cf. A136521, A028387. %K A143956 nonn,tabl %O A143956 1,2 %A A143956 _Gary W. Adamson_ & _Roger L. Bagula_, Aug 26 2008