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 A221987 #9 Feb 04 2013 21:56:55
%S A221987 1,1,1,1,4,1,1,11,11,1,1,26,62,26,1,1,57,274,274,57,1,1,120,1063,2024,
%T A221987 1063,120,1,1,247,3805,12411,12411,3805,247,1,1,502,12916,67882,
%U A221987 113414,67882,12916,502,1,1,1013,42284,343700,891930,891930,343700,42284,1013,1
%N A221987 G.f.: A(x,y) = Sum_{n>=0} n!*x^n*y^n * Product_{k=1..n} (1+y + 2*k*x*y) / (1 + (1+y)*k*x + 2*k^2*x^2*y).
%H A221987 Paul D. Hanna, <a href="/A221987/b221987.txt">Rows n=0..31, flattened.</a>
%F A221987 Row sums equal A221988.
%e A221987 Triangle begins:
%e A221987 1;
%e A221987 1, 1;
%e A221987 1, 4, 1;
%e A221987 1, 11, 11, 1;
%e A221987 1, 26, 62, 26, 1;
%e A221987 1, 57, 274, 274, 57, 1;
%e A221987 1, 120, 1063, 2024, 1063, 120, 1;
%e A221987 1, 247, 3805, 12411, 12411, 3805, 247, 1;
%e A221987 1, 502, 12916, 67882, 113414, 67882, 12916, 502, 1;
%e A221987 1, 1013, 42284, 343700, 891930, 891930, 343700, 42284, 1013, 1;
%e A221987 1, 2036, 134981, 1646808, 6339786, 9718184, 6339786, 1646808, 134981, 2036, 1; ...
%o A221987 (PARI) {T(n, k)=polcoeff(polcoeff( sum(m=0, n, m!*x^m*prod(k=1, m, (1+y+2*k*x*y)/(1+(1+y)*k*x+2*k^2*x^2*y +x*O(x^n))) ), n, x), k, y)}
%o A221987 for(n=0, 12, for(k=0, n, print1(T(n, k), ", ")); print(""))
%Y A221987 Cf. A221988, A136126, A221971.
%K A221987 nonn,tabl
%O A221987 0,5
%A A221987 _Paul D. Hanna_, Feb 02 2013