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 A124730 #5 Mar 03 2013 13:48:24 %S A124730 1,1,2,1,6,2,1,14,8,4,1,30,22,24,4,1,62,52,92,28,8,1,126,114,288,120, %T A124730 72,8,1,254,240,804,408,384,80,16,1,510,494,2088,1212,1584,46,192,16 %N A124730 Triangle, row sums = powers of 3. %C A124730 In A124731, we switch the diagonals. In both triangles, row sums = powers of 3. %F A124730 Let M = the infinite bidiagonal matrix with (1,2,1,2...) in the main diagonal and (2,1,2,1...) in the subdiagonal. The n-th row of the triangle (extracting the zeros) = M^n * [1,0,0,0...]. %e A124730 Row 2 = (1, 6, 2) since [1,0,0; 2,2,0; 0,1,1]^2 * [1,0,0] = [1,6,2]. %e A124730 First few rows of the triangle are: %e A124730 1; %e A124730 1, 2; %e A124730 1, 6, 2; %e A124730 1, 14, 8, 4; %e A124730 1, 30, 22, 24, 4; %e A124730 1, 62, 52, 92, 28, 8; %e A124730 1, 126, 114, 288, 120, 72, 8; %e A124730 ... %Y A124730 Cf. A124731, A124732. %K A124730 nonn,tabl %O A124730 0,3 %A A124730 _Gary W. Adamson_ & _Roger L. Bagula_, Nov 05 2006