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 A109000 #4 Mar 30 2012 18:36:49
%S A109000 1,1,3,11,37,133,479,1719,6121,21609,75675,263171,909899,3130963,
%T A109000 10730891,36639987,124528283,420319907,1403656123,4615627555,
%U A109000 14868713515,46702912307,142489152555,421113970835,1203581558011
%N A109000 Antidiagonal sums of square array A108998, in which row n equals the coordination sequence of B_n lattice.
%C A109000 Limit a(n+1)/a(n) ~ 3.3829757679..., real root of cubic (1+x+3*x^2-x^3). Compare to antidiagonal sums A108555 of square array A108553, in which row n equals the crystal ball sequence for D_n lattice.
%F A109000 a(n) = Sum_{k=0..n} Sum_{j=0..k} C(n-j-1, k-j) * (C(2*n-2*k+1, 2*j)-2*(n-k)*C(n-k-1, j-1)).
%o A109000 (PARI) {a(n)=sum(k=0,n,sum(j=0,k, binomial(n-j-1,k-j)*(binomial(2*n-2*k+1,2*j)-2*(n-k)*binomial(n-k-1,j-1))))}
%Y A109000 Cf. A108998, A108999, A109001.
%K A109000 nonn
%O A109000 0,3
%A A109000 _Paul D. Hanna_, Jun 17 2005