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Matula-Goebel numbers of rooted trees whose number of leaves equals their number of internal (non-leaf) nodes.
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%I #9 Nov 25 2022 16:41:43

%S 2,6,7,18,20,21,26,34,37,43,54,60,63,67,70,78,88,91,92,95,102,111,116,

%T 119,122,129,142,146,151,162,164,173,180,181,189,200,201,202,210,227,

%U 234,236,239,245,260,264,269,273,276,278,285,306,308,314,322,333,337

%N Matula-Goebel numbers of rooted trees whose number of leaves equals their number of internal (non-leaf) nodes.

%C The Matula-Goebel number of a rooted tree is the product of primes indexed by the Matula-Goebel numbers of the branches of its root, which gives a bijective correspondence between positive integers and unlabeled rooted trees.

%H Gus Wiseman, <a href="/A358578/a358578.png">The first 64 rooted trees whose number of leaves equals their number of internal nodes.</a>

%F A342507(a(n)) = A109129(a(n)).

%e The terms together with their corresponding rooted trees begin:

%e 2: (o)

%e 6: (o(o))

%e 7: ((oo))

%e 18: (o(o)(o))

%e 20: (oo((o)))

%e 21: ((o)(oo))

%e 26: (o(o(o)))

%e 34: (o((oo)))

%e 37: ((oo(o)))

%e 43: ((o(oo)))

%e 54: (o(o)(o)(o))

%e 60: (oo(o)((o)))

%e 63: ((o)(o)(oo))

%e 67: (((ooo)))

%e 70: (o((o))(oo))

%e 78: (o(o)(o(o)))

%e 88: (ooo(((o))))

%e 91: ((oo)(o(o)))

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

%t Select[Range[100],Count[MGTree[#],{},{0,Infinity}]==Count[MGTree[#],_[__],{0,Infinity}]&]

%Y These trees are counted by A185650, ordered A358579.

%Y Height instead of leaves: A358576, counted by A358587, ordered A358588.

%Y Height instead of internals: A358577, counted by A358589, ordered A358590.

%Y Positions of 0's in A358580.

%Y A000081 counts rooted trees, ordered A000108.

%Y A034781 counts trees by nodes and height.

%Y A055277 counts trees by nodes and leaves, ordered A001263.

%Y MG statistics: A061775, A109082, A109129, A196050, A342507, A358552.

%Y Cf. A000040, A000720, A001222, A007097, A056239, A112798.

%Y Cf. A206487, A358371, A358581-A358586, A358592.

%K nonn

%O 1,1

%A _Gus Wiseman_, Nov 25 2022