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 A117352 #2 Mar 30 2012 18:59:14
%S A117352 1,2,1,4,1,1,8,1,0,1,16,1,-1,-1,1,32,1,-2,-2,-2,1,64,1,-3,-2,-2,-3,1,
%T A117352 128,1,-4,-1,0,-1,-4,1,256,1,-5,1,3,3,1,-5,1,512,1,-6,4,6,6,6,4,-6,1,
%U A117352 1024,1,-7,8,8,6,6,8,8,-7,1
%N A117352 Riordan array (1/(1-2x), x(1-2x)/(1-x)).
%C A117352 Row sums are A038505. Diagonal sums are A117353. Inverse is A117354.
%F A117352 Number triangle T(n,k)=sum{j=0..n-k, C(j-k,j)C(n-k,j)}
%e A117352 Triangle begins
%e A117352 1,
%e A117352 2, 1,
%e A117352 4, 1, 1,
%e A117352 8, 1, 0, 1,
%e A117352 16, 1, -1, -1, 1,
%e A117352 32, 1, -2, -2, -2, 1,
%e A117352 64, 1, -3, -2, -2, -3, 1
%K A117352 easy,sign,tabl
%O A117352 0,2
%A A117352 _Paul Barry_, Mar 09 2006