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 A181650 #16 Aug 26 2021 21:28:10 %S A181650 1,-1,1,-1,0,1,0,0,-1,1,0,0,-1,0,1,0,0,0,0,-1,1,0,0,0,0,-1,0,1,0,0,0, %T A181650 0,0,0,-1,1,0,0,0,0,0,0,-1,0,1,0,0,0,0,0,0,0,0,-1,1,0,0,0,0,0,0,0,0, %U A181650 -1,0,1 %N A181650 Inverse of number triangle A070909. %C A181650 Generalized (conditional) Riordan array with k-th column generated by x^k*(1-x-x^2) if k is even, x^k otherwise. %C A181650 Triangle T(n,k), read by rows, given by (-1,2,-1/2,-1/2,0,0,0,0,0,0,0,...) DELTA (1,0,-1,0,0,0,0,0,0,0,0,0,...) where DELTA is the operator defined in A084938. - _Philippe Deléham_, Nov 19 2011 %C A181650 Double Riordan array (1 - x - x^2; x/(1 - x - x^2), x*(1 - x - x^2)) as defined in Davenport et al. - _Peter Bala_, Aug 15 2021 %H A181650 D. E. Davenport, L. W. Shapiro and L. C. Woodson, <a href="https://doi.org/10.37236/2034">The Double Riordan Group</a>, The Electronic Journal of Combinatorics, 18(2) (2012). %F A181650 G.f.: (1+(y-1)*x-x^2)/((1-y*x)*(1+y*x)). - _Philippe Deléham_, Nov 19 2011 %e A181650 Triangle begins %e A181650 1, %e A181650 -1, 1, %e A181650 -1, 0, 1, %e A181650 0, 0, -1, 1, %e A181650 0, 0, -1, 0, 1, %e A181650 0, 0, 0, 0, -1, 1, %e A181650 0, 0, 0, 0, -1, 0, 1, %e A181650 0, 0, 0, 0, 0, 0, -1, 1, %e A181650 0, 0, 0, 0, 0, 0, -1, 0, 1, %e A181650 0, 0, 0, 0, 0, 0, 0, 0, -1, 1, %e A181650 0, 0, 0, 0, 0, 0, 0, 0, -1, 0, 1 %e A181650 Production matrix begins %e A181650 -1, 1, %e A181650 -2, 1, 1, %e A181650 -1, 1, -1, 1, %e A181650 -1, 1, -2, 1, 1, %e A181650 -1, 1, -1, 1, -1, 1, %e A181650 -1, 1, -1, 1, -2, 1, 1, %e A181650 -1, 1, -1, 1, -1, 1, -1, 1, %e A181650 -1, 1, -1, 1, -1, 1, -2, 1, 1, %e A181650 -1, 1, -1, 1, -1, 1, -1, 1, -1, 1 %Y A181650 Cf. A084221, A084938. %K A181650 easy,sign,tabl %O A181650 0,1 %A A181650 _Paul Barry_, Nov 03 2010