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 A108557 #6 Jun 13 2017 02:02:34 %S A108557 1,3,9,63,433,2823,17657,107439,642529,3802167,22357097,130970271, %T A108557 765564049,4469342439,26073165401,152043343119,886424978881, %U A108557 5167271805207,30119654732489,175558462395135,1023255914549617 %N A108557 Row sums of triangle A108556, in which row n equals the inverse binomial transform of the crystal ball sequence for D_n lattice. %C A108557 Limit a(n+1)/a(n) = 3+sqrt(8) = 5.82842712... %F A108557 G.f.: (1-9*x+19*x^2+33*x^3-80*x^4+12*x^5)/(1-12*x+46*x^2-60*x^3+9*x^4). %o A108557 (PARI) a(n)=local(A=vector(n+1,r,vector(n+1,c,if(r-1==0 || c-1==0,1,if(r-1==1,2*c-1, sum(j=0,c-1,binomial(r+c-j-2,c-j-1)*(binomial(2*r-2,2*j)-2*(r-1)*binomial(r-3,j-1)))))))); sum(k=0,n,polcoeff(subst(Ser(A[n+1]),x, x/(1+x))/(1+x),k)) %Y A108557 Cf. A108553, A108556. %K A108557 nonn,easy %O A108557 0,2 %A A108557 _Paul D. Hanna_, Jun 10 2005