

A184155


The MatulaGoebel number of rooted trees having all leaves at the same level.


7



1, 2, 3, 4, 5, 7, 8, 9, 11, 16, 17, 19, 21, 23, 25, 27, 31, 32, 49, 53, 57, 59, 63, 64, 67, 73, 81, 83, 85, 97, 103, 115, 121, 125, 127, 128, 131, 133, 147, 159, 171, 189, 227, 241, 243, 256, 269, 277, 289, 307, 311, 331, 335, 343, 361, 365, 367, 371, 391, 393, 399, 419, 425, 431, 439, 441, 477
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OFFSET

1,2


COMMENTS

The MatulaGoebel number of a rooted tree can be defined in the following recursive manner: to the onevertex tree there corresponds the number 1; to a tree T with root degree 1 there corresponds the tth prime number, where t is the MatulaGoebel number of the tree obtained from T by deleting the edge emanating from the root; to a tree T with root degree m>=2 there corresponds the product of the MatulaGoebel numbers of the m branches of T.
The sequence is infinite.


REFERENCES

F. Goebel, On a 11correspondence between rooted trees and natural numbers, J. Combin. Theory, B 29 (1980), 141143.
I. Gutman and A. Ivic, On Matula numbers, Discrete Math., 150, 1996, 131142.
I. Gutman and YeongNan Yeh, Deducing properties of trees from their Matula numbers, Publ. Inst. Math., 53 (67), 1993, 1722.
D. W. Matula, A natural rooted tree enumeration by prime factorization, SIAM Review, 10, 1968, 273.


LINKS

Table of n, a(n) for n=1..67.
Index entries for sequences related to MatulaGoebel numbers


FORMULA

In A184154 one constructs for each n the generating polynomial P(n,x) of the leaves of the rooted tree with MatulaGoebel number n, according to their levels. The Maple program finds those n (between 1 and 500) for which P(n,x) is a monomial.


EXAMPLE

7 is in the sequence because the rooted tree with MatulaGoebel number 7 is the rooted tree Y, having all leaves at level 2.
2^m is in the sequence for each positive integer m because the rooted tree with MatulaGoebel number 2^m is a star with m edges.
From Gus Wiseman, Mar 30 2018: (Start)
Sequence of trees begins:
01 o
02 (o)
03 ((o))
04 (oo)
05 (((o)))
07 ((oo))
08 (ooo)
09 ((o)(o))
11 ((((o))))
16 (oooo)
17 (((oo)))
19 ((ooo))
21 ((o)(oo))
23 (((o)(o)))
25 (((o))((o)))
27 ((o)(o)(o))
31 (((((o)))))
(End)


MAPLE

with(numtheory): P := proc (n) local r, s: r := proc (n) options operator, arrow: op(1, factorset(n)) end proc: s := proc (n) options operator, arrow: n/r(n) end proc: if n = 1 then 1 elif bigomega(n) = 1 then sort(expand(x*P(pi(n)))) else sort(P(r(n))+P(s(n))) end if end proc: A := {}: for n to 500 do if degree(numer(subs(x = 1/x, P(n)))) = 0 then A := `union`(A, {n}) else end if end do: A;


MATHEMATICA

primeMS[n_]:=If[n===1, {}, Flatten[Cases[FactorInteger[n], {p_, k_}:>Table[PrimePi[p], {k}]]]];
dep[n_]:=If[n===1, 0, 1+Max@@dep/@primeMS[n]];
rnkQ[n_]:=And[SameQ@@dep/@primeMS[n], And@@rnkQ/@primeMS[n]];
Select[Range[2000], rnkQ] (* Gus Wiseman, Mar 30 2018 *)


CROSSREFS

Cf. A000081, A003238, A004111, A007097, A048816, A061775, A109082, A184154, A214577, A244925, A276625, A290689, A290760, A290822, A298422, A298424, A298426.
Sequence in context: A316468 A099627 A324841 * A331913 A318612 A318690
Adjacent sequences: A184152 A184153 A184154 * A184156 A184157 A184158


KEYWORD

nonn


AUTHOR

Emeric Deutsch, Oct 07 2011


STATUS

approved



