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 A117179 #13 Jun 05 2017 03:49:23 %S A117179 1,0,1,-3,0,1,0,-4,0,1,5,0,-5,0,1,0,9,0,-6,0,1,-7,0,14,0,-7,0,1,0,-16, %T A117179 0,20,0,-8,0,1,9,0,-30,0,27,0,-9,0,1,0,25,0,-50,0,35,0,-10,0,1,-11,0, %U A117179 55,0,-77,0,44,0,-11,0,1 %N A117179 Riordan array ((1-x^2)/(1+x^2)^2,x/(1+x^2)). %C A117179 Inverse is A117178. Row sums are (-1)^n*A098554(n+1). Diagonal sums are 1,0,-2,0,2,0,-2,... with g.f. (1-x^2)/(1+x^2). %C A117179 Apparently, with the rows de-aerated and then reversed, this matrix becomes signed A034807 with the twos on the diagonal removed. Apparently, |D(2n,k+1)| = |D(2(n-1),k+1)| + |D(2n,k)| where D(n,k) is the k-th element on the n-th diagonal. - _Tom Copeland_, May 30 2017 %e A117179 Triangle begins %e A117179 1, %e A117179 0, 1, %e A117179 -3, 0, 1, %e A117179 0, -4, 0, 1, %e A117179 5, 0, -5, 0, 1, %e A117179 0, 9, 0, -6, 0, 1, %e A117179 -7, 0, 14, 0, -7, 0, 1, %e A117179 0, -16, 0, 20, 0, -8, 0, 1 %K A117179 easy,sign,tabl %O A117179 0,4 %A A117179 _Paul Barry_, Mar 01 2006