A058518 - OEIS

%I #4 Mar 30 2012 16:48:55

%S 1,1,1,2,2,4,6,9,14,21,33,54,89,142,222,350,554,883,1406,2225,3511,

%T 5539,8768,13977,22417,36143,58483,94818,153716,248699,401054,644485,

%U 1032794,1652377,2642421,4227547,6769660,10851491,17410292,27951747

%N Number of forests of B-trees of order 3 with n labeled leaves.

%p spec := [C, {B=Union(Z, Subst(M, B)), M=Union(Prod(Z,Z),Prod(Z,Z,Z)), C=PowerSet(B)} ]; [seq(combstruct[count](spec, size=n), n=0..40)];

%Y Cf. A014535.

%K nonn

%O 0,4

%A _N. J. A. Sloane_, Dec 21 2000