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 A104571 #5 Mar 30 2012 17:25:11 %S A104571 1,4,1,5,4,1,8,5,4,1,9,8,5,4,1,12,9,8,5,4,1,13,12,9,8,5,4,1,16,13,12, %T A104571 9,8,5,4,1 %N A104571 Triangle T(n,k) = A042948(n-k+1) read by rows, 0<=k<=n. %F A104571 The triangle is extracted from the product of lower triangular matrices (with the rest of the terms all zeros): G * R (or R * G); G = [1; 3, 1; 1, 3, 1; 3, 1, 3, 1;...]; R = [1; 1, 1; 1, 1, 1;...]. %e A104571 The first few rows are: %e A104571 1; %e A104571 4, 1; %e A104571 5, 4, 1; %e A104571 8, 5, 4, 1; %e A104571 9, 8, 5, 4, 1; %e A104571 ... %Y A104571 Cf. A042948, A035608 (row sums), A104570, A104569, A074377. %K A104571 nonn,tabl,easy %O A104571 0,2 %A A104571 _Gary W. Adamson_, Mar 16 2005