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 A117372 #3 Mar 30 2012 18:59:14 %S A117372 1,-3,1,0,-4,1,0,3,-5,1,0,0,7,-6,1,0,0,-3,12,-7,1,0,0,0,-10,18,-8,1,0, %T A117372 0,0,3,-22,25,-9,1,0,0,0,0,13,-40,33,-10,1,0,0,0,0,-3,35,-65,42,-11,1, %U A117372 0,0,0,0,0,-16,75,-98,52,-12,1 %N A117372 Riordan array (1-3x,x(1-x)). %C A117372 Row sums are A117373. Diagonal sums are A117374. Inverse is A117375. %F A117372 Number triangle T(n,k)=(-1)^(n-k)(C(k,n-k)+3*C(k, n-k-1)) %e A117372 Triangle begins %e A117372 1, %e A117372 -3, 1, %e A117372 0, -4, 1, %e A117372 0, 3, -5, 1, %e A117372 0, 0, 7, -6, 1, %e A117372 0, 0, -3, 12, -7, 1, %e A117372 0, 0, 0, -10, 18, -8, 1, %e A117372 0, 0, 0, 3, -22, 25, -9, 1 %K A117372 easy,sign,tabl %O A117372 0,2 %A A117372 _Paul Barry_, Mar 10 2006