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 A181654 #10 Nov 20 2022 10:52:39 %S A181654 1,1,1,2,1,1,3,2,1,1,6,4,2,1,1,9,6,3,2,1,1,18,12,6,4,2,1,1,27,18,9,6, %T A181654 3,2,1,1,54,36,18,12,6,4,2,1,1,81,54,27,18,9,6,3,2,1,1,162,108,54,36, %U A181654 18,12,6,4,2,1,1 %N A181654 An eigentriangle of the number triangle A181653. %C A181654 Generalized (conditional) Riordan array with k-th column generated by x^k*if(mod(k,2)=0,(1+x-x^2)/(1-3x^2),(1+x-x^2+x^3)/(1-3x^2)). %C A181654 Row sums are A181655. %H A181654 Paul Barry, <a href="http://arxiv.org/abs/1107.5490">Invariant number triangles, eigentriangles and Somos-4 sequences</a>, arXiv preprint arXiv:1107.5490 [math.CO], 2011. %e A181654 Triangle begins %e A181654 1, %e A181654 1, 1, %e A181654 2, 1, 1, %e A181654 3, 2, 1, 1, %e A181654 6, 4, 2, 1, 1, %e A181654 9, 6, 3, 2, 1, 1, %e A181654 18, 12, 6, 4, 2, 1, 1, %e A181654 27, 18, 9, 6, 3, 2, 1, 1, %e A181654 54, 36, 18, 12, 6, 4, 2, 1, 1, %e A181654 81, 54, 27, 18, 9, 6, 3, 2, 1, 1, %e A181654 162, 108, 54, 36, 18, 12, 6, 4, 2, 1, 1 %K A181654 easy,nonn,tabl %O A181654 0,4 %A A181654 _Paul Barry_, Nov 03 2010