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 A158687 #11 Apr 21 2015 04:47:30
%S A158687 1,1,1,1,4,1,1,8,7,1,1,12,24,10,1,1,16,56,49,13,1,1,20,104,160,83,16,
%T A158687 1,1,24,168,400,351,126,19,1,1,28,248,832,1120,656,178,22,1,1,32,344,
%U A158687 1520,2912,2561,1102,239,25,1
%N A158687 Riordan array (1/(1-x),x(1+x)^2/(1-x)).
%C A158687 Row sums are A077936. Diagonal sums are A129847. Central terms are A059304.
%C A158687 Inverse of alternating signed version is A100326.
%F A158687 Number triangle T(n,k) = Sum_{j=0..n-k} C(n-j,k)*C(2k,j).
%F A158687 T(n,k) = T(n-1,k) + T(n-1,k-1) + 2*T(n-2,k-1) + T(n-3,k-1), T(0,0) = T(1,0) = T(1,1) = 1, T(n,k) = 0 if k<0 or if k>n. - _Philippe Deléham_, Nov 11 2013
%F A158687 G.f.: 1/(1-y-x*(1+y)^2). - _Vladimir Kruchinin_, Apr 21 2015
%e A158687 Number triangle begins
%e A158687 1,
%e A158687 1, 1,
%e A158687 1, 4, 1,
%e A158687 1, 8, 7, 1,
%e A158687 1, 12, 24, 10, 1,
%e A158687 1, 16, 56, 49, 13, 1,
%e A158687 1, 20, 104, 160, 83, 16, 1
%Y A158687 Cf. A059304, A077936, A100326, A129847.
%K A158687 easy,nonn,tabl
%O A158687 0,5
%A A158687 _Paul Barry_, Mar 24 2009