OFFSET
0,5
LINKS
Eric Weisstein's World of Mathematics, B-tree
FORMULA
G.f. A(x) satisfies: A(x) = x + A(x^2+x^3+x^4). [Geoffrey Critzer, Mar 28 2013]
MAPLE
spec := [ B, {B=Union(Z, Subst(M, B)), M=Union(Prod(Z, Z), Prod(Z, Z, Z), Prod(Z$4))} ]: [ seq(combstruct[count](spec, size=n), n=0..42) ];
MATHEMATICA
nn=38; f[x_]:=Sum[a[n]x^n, {n, 0, nn}]; a[0]=0; sol=SolveAlways[0==Series[f[x]-x-f[x^2+x^3+x^4], {x, 0, nn}], x]; Table[a[n], {n, 0, nn}]/.sol (* Geoffrey Critzer, Mar 28 2013 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
STATUS
approved