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 A219557 #9 Nov 29 2012 19:44:48
%S A219557 1,3,9,33,96,273,749,1953,4916,12023,28642,66575,151544,338294,741880,
%T A219557 1601048,3403936,7137386,14774713,30219025,61115184,122300146,
%U A219557 242312186,475589389,925158391,1784529840,3414565313,6483608230,12221370425,22876263089,42534593868
%N A219557 Sum of numbers of bipartite partitions of (n,k) into distinct pairs for 0<=k<=n.
%H A219557 Alois P. Heinz, <a href="/A219557/b219557.txt">Table of n, a(n) for n = 0..80</a>
%F A219557 a(n) = Sum_{k=0..n} [x^n*y^k] 1/2 * Product_{i,j>=0} (1+x^i*y^j).
%e A219557 a(2) = 9: [(2,0)], [(2,1)], [(2,0),(0,1)], [(1,1),(1,0)], [(2,2)], [(2,1),(0,1)], [(2,0),(0,2)], [(1,2),(1,0)], [(1,1),(1,0),(0,1)].
%Y A219557 Row sums of A201377.
%K A219557 nonn
%O A219557 0,2
%A A219557 _Alois P. Heinz_, Nov 22 2012