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 A037026 B-trees of order 4 with n leaves. 4

%I

%S 0,1,1,1,2,2,4,5,9,15,28,45,73,116,199,345,601,1021,1738,2987,5244,

%T 9321,16720,30103,54345,97996,176011,314045,556577,980852,1722451,

%U 3020214,5298570,9316456,16440262,29136489,51860214,92643425,165934156

%N B-trees of order 4 with n leaves.

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/B-Tree.html">B-tree</a>

%H <a href="/index/Ro#rooted">Index entries for sequences related to rooted trees</a>

%F G.f. A(x) satisfies: A(x) = x + A(x^2+x^3+x^4). [_Geoffrey Critzer_, Mar 28 2013]

%p 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) ];

%t 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 *)

%Y Cf. A014535.

%K nonn

%O 0,5

%A _N. J. A. Sloane_, _Paul Zimmermann_

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Last modified June 21 06:55 EDT 2021. Contains 345358 sequences. (Running on oeis4.)