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Matula-Goebel numbers of leaf-balanced trees.
13

%I #6 Sep 01 2017 05:02:33

%S 1,2,3,4,5,6,7,8,9,10,11,12,13,15,16,17,18,19,20,22,23,24,25,27,29,30,

%T 31,32,33,36,37,40,41,44,45,47,48,49,50,53,54,55,59,60,61,62,64,66,67,

%U 71,72,75,79,80,81,83,88,89,90,91,93,96,97,99,100,103,108

%N Matula-Goebel numbers of leaf-balanced trees.

%C An unlabeled rooted tree is leaf-balanced if every branch has the same number of leaves and every non-leaf rooted subtree is also leaf-balanced.

%t nn=2000;

%t primeMS[n_]:=If[n===1,{},Flatten[Cases[FactorInteger[n],{p_,k_}:>Table[PrimePi[p],{k}]]]];

%t leafcount[n_]:=If[n===1,1,With[{m=primeMS[n]},If[Length[m]===1,leafcount[First[m]],Total[leafcount/@m]]]];

%t balQ[n_]:=Or[n===1,With[{m=primeMS[n]},And[SameQ@@leafcount/@m,And@@balQ/@m]]];

%t Select[Range[nn],balQ]

%Y Cf. A000081, A007097, A061775, A109129, A214577, A280994, A291441, A291443.

%K nonn

%O 1,2

%A _Gus Wiseman_, Aug 23 2017