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 A056589 #4 Mar 31 2012 13:20:04 %S A056589 1,4,16,53,166,492,1413,3960,10912,29689,80026,214196,570289,1512300, %T A056589 3998160,10545741,27766942,73012060,191785165,503378480,1320425536, %U A056589 3462057009,9074076786,23776857828,62289901081,163159711492 %N A056589 Third column sequence of unsigned triangle A056588. %F A056589 a(n)= -A056588(n+2, 2), n >= 0. a(n)= -2^(n+3)+F(n+4)*(F(n+3)+1), F(n)=A000045(n). %F A056589 G.f.(1-x+x^2)/((1-2*x)*(1+x)*(1-3*x+x^2)*(1-x-x^2)) %Y A056589 Cf. A000045, A056588, A000012, A000071. %K A056589 nonn,easy %O A056589 0,2 %A A056589 _Wolfdieter Lang_ Jul 10 2000