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 A117355 #9 Jan 17 2014 04:25:44
%S A117355 1,0,1,1,0,1,0,0,0,1,1,0,-1,0,1,0,-1,0,-2,0,1,1,0,-2,0,-3,0,1,0,-2,0,
%T A117355 -2,0,-4,0,1,1,0,-2,0,-1,0,-5,0,1,0,-3,0,0,0,1,0,-6,0,1,1,0,-1,0,3,0,
%U A117355 4,0,-7,0,1,0,-4,0,3,0,6,0,8,0,-8,0,1,1,0,1,0,6,0,8,0,13,0,-9,0,1
%N A117355 Riordan array (1/(1-x^2),x(1-2x^2)/(1-x^2)).
%C A117355 Row sums are A077948.
%C A117355 Diagonal sums are the aerated version of A009545 with g.f. 1/(1-2x^2+2x^4).
%F A117355 Number triangle T(n,k)=sum{j=0..n-k, C(j-(n-k)/2-1,j)C(k,j)(1+(-1)^(n-k))/2}
%F A117355 T(n,k)=T(n-1,k-1)+T(n-2,k)-2*T(n-3,k-1), T(0,0)=T(1,1)=T(2,0)=T(2,2)=1, T(1,1)=T(2,1)=0, T(n,k)=0 if k<0 or if k>n. - _Philippe Deléham_, Jan 16 2014
%e A117355 Triangle begins
%e A117355 1,
%e A117355 0, 1,
%e A117355 1, 0, 1,
%e A117355 0, 0, 0, 1,
%e A117355 1, 0, -1, 0, 1,
%e A117355 0, -1, 0, -2, 0, 1,
%e A117355 1, 0, -2, 0, -3, 0, 1,
%e A117355 0, -2, 0, -2, 0, -4, 0, 1
%K A117355 easy,sign,tabl
%O A117355 0,19
%A A117355 _Paul Barry_, Mar 09 2006