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 A037026 B-trees of order 4 with n leaves. 4
 0, 1, 1, 1, 2, 2, 4, 5, 9, 15, 28, 45, 73, 116, 199, 345, 601, 1021, 1738, 2987, 5244, 9321, 16720, 30103, 54345, 97996, 176011, 314045, 556577, 980852, 1722451, 3020214, 5298570, 9316456, 16440262, 29136489, 51860214, 92643425, 165934156 (list; graph; refs; listen; history; text; internal format)
 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 Cf. A014535. Sequence in context: A230380 A127968 A188541 * A116651 A135586 A168542 Adjacent sequences:  A037023 A037024 A037025 * A037027 A037028 A037029 KEYWORD nonn AUTHOR STATUS approved

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Last modified October 13 18:57 EDT 2019. Contains 327981 sequences. (Running on oeis4.)