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 A055219 #7 Mar 30 2012 18:57:04 %S A055219 1,5,21,78,274,927,3061,9933,31824,100972,317942,995088,3099105, %T A055219 9612735,29715525,91595391,281643480,864189486,2646805668,8093543439, %U A055219 24713953515,75370741506,229604257846,698754428388,2124616182139 %N A055219 T(2n+3,n), array T as in A055216. %F A055219 Apparently a(n)=sum((-1)^j*binomial(n+3, j)*binomial(2n+3-3j, n+3), j=0..floor(n/3)). - _Emeric Deutsch_, Mar 13 2004 %K A055219 nonn %O A055219 0,2 %A A055219 _Clark Kimberling_, May 07 2000