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 A116949 #13 Oct 17 2023 11:16:48 %S A116949 1,0,1,-2,0,1,-1,-2,0,1,4,-1,-2,0,1,2,4,-1,-2,0,1,-8,2,4,-1,-2,0,1,-4, %T A116949 -8,2,4,-1,-2,0,1,16,-4,-8,2,4,-1,-2,0,1,8,16,-4,-8,2,4,-1,-2,0,1,-32, %U A116949 8,16,-4,-8,2,4,-1,-2,0,1,-16,-32,8,16,-4,-8,2,4,-1,-2,0,1,64,-16,-32,8,16,-4,-8,2,4,-1,-2,0,1 %N A116949 Riordan array ((1-x^3)/(1+2x^2),x). %C A116949 Sequence array of (-2)^(n/2)(1+(-1)^n)/2-(-2)^((n-3)/2)(1-(-1)^n)/2-(comb(1,n)-comb(0,n))/2. %C A116949 Inverse of A116948. %C A116949 Row sums are A117575. Diagonal sums are A117576. %e A116949 Number triangle begins %e A116949 1, %e A116949 0, 1, %e A116949 -2, 0, 1, %e A116949 -1, -2, 0, 1, %e A116949 4, -1, -2, 0, 1, %e A116949 2, 4, -1, -2, 0, 1, %e A116949 -8, 2, 4, -1, -2, 0, 1, %e A116949 -4, -8, 2, 4, -1, -2, 0, 1, %e A116949 16, -4, -8, 2, 4, -1, -2, 0, 1 %Y A116949 Cf. A117575, A117576, A116948. %K A116949 easy,sign,tabl %O A116949 0,4 %A A116949 _Paul Barry_, Mar 29 2006 %E A116949 Entry revised by _N. J. A. Sloane_, Apr 10 2006