

A212627


Irregular triangle read by rows: T(n,k) is the number of maximal independent vertex subsets with k vertices of the rooted tree with MatulaGoebel number n (n>=1, k>=1).


11



1, 2, 1, 1, 1, 1, 0, 3, 0, 3, 1, 0, 1, 1, 0, 1, 0, 3, 1, 0, 3, 1, 0, 3, 1, 0, 1, 2, 0, 1, 2, 0, 1, 2, 0, 1, 4, 1, 0, 0, 1, 0, 1, 2, 0, 0, 5, 1, 0, 0, 1, 0, 2, 1, 1, 0, 2, 1, 1, 0, 1, 4, 0, 0, 5, 0, 1, 0, 2, 0, 0, 6, 1, 0, 0, 5, 0, 0, 7, 1, 0, 0, 2, 1, 0, 2, 1, 1, 0, 0, 4, 2, 0, 1, 4, 1, 0, 0, 0, 1, 0, 0, 6, 1, 0, 2, 1, 1, 0, 1, 1, 3, 0, 0, 1, 4, 0, 1, 0, 2, 0, 1, 0, 2, 0, 0, 4, 2, 0, 2, 0, 1, 1, 0, 0, 5, 0, 0, 2, 3, 0, 0, 2, 1, 0, 1, 1, 3, 0, 0, 3, 6
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OFFSET

1,2


COMMENTS

A vertex subset in a tree is said to be independent if no pair of vertices is connected by an edge. The empty set is considered to be independent. An independent vertex subset S of a tree is said to be maximal if every vertex that is not in S is joined by an edge to at least one vertex of S.
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.
Number of entries in row n is A212625(n).
Sum of entries in row n = A212628(n).
Sum(k*T(n,k), k>=1) = A212629(n).


REFERENCES

F. Goebel, On a 11 correspondence 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 YN. 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.
É. Czabarka, L. Székely, and S. Wagner, The inverse problem for certain tree parameters, Discrete Appl. Math., 157, 2009, 33143319.
H. S. Wilf, The number of maximal independent sets in a tree, SIAM J. Alg. Disc. Math., 7, 1986, 125130.


LINKS

Table of n, a(n) for n=1..152.
E. Deutsch, Rooted tree statistics from Matula numbers, arXiv:1111.4288.
Index entries for sequences related to MatulaGoebel numbers


FORMULA

Let A(n)=A(n,x), B(n)=B(n,x), C(n)=C(n,x) be the generating polynomial with respect to size of the maximal independent sets that contain the root, the maximal independent sets that do not contain the root, and the independent sets which are not maximal but become maximal if the root is removed, respectively. We have : A(1)=x, B(1)=0, C(1)=1, A(tth prime) = x[B(t) + C(t)], B(tth prime) = A(t), C(tth prime)=B(t), A(rs)=A(r)A(s)/x, B(rs)=B(r)B(s)+B(r)C(s)+B(s)C(r), C(rs)=C(r)C(s) (r,s>=2). The generating polynomial of the maximal independent vertex subsets of the r oo ted tree with MatulaGoebel number n, with respect to number of vertices, is P(n)=P(n,x)=A(n)+B(n). The Maple program is based on these relations.


EXAMPLE

Row 11 is 0, 3, 1 because the rooted tree with MatulaGoebel number 11 is the path tree on 5 vertices R  A  B  C  D; the maximal independent vertex subsets are {R,C}, {A,C}, {A,D}, and {R,B,D}, i.e. none of size 1, three of size 2, and one of size 3.
Triangle starts:
1;
2;
1,2;
1,1;
0,3;


MAPLE

with(numtheory): P := proc (n) local r, s, A, B, C: r := proc (n) options operator, arrow: op(1, factorset(n)) end proc: s := proc (n) options operator, arrow: n/r(n) end proc: A := proc (n) if n = 1 then x elif bigomega(n) = 1 then x*(B(pi(n))+C(pi(n))) else A(r(n))*A(s(n))/x end if end proc: B := proc (n) if n = 1 then 0 elif bigomega(n) = 1 then A(pi(n)) else sort(expand(B(r(n))*B(s(n))+B(r(n))*C(s(n))+B(s(n))*C(r(n)))) end if end proc: C := proc (n) if n = 1 then 1 elif bigomega(n) = 1 then B(pi(n)) else expand(C(r(n))*C(s(n))) end if end proc: if n = 1 then x else sort(expand(A(n)+B(n))) end if end proc: for n to 12 do seq(coeff(P(n), x, j), j = 1 .. degree(P(n))) end do; # yields sequence in triangular form


CROSSREFS

Cf. A212618, A212619, A212620, A212621, A212622, A212623, A212624, A212625, A212626, A212628, A212629, A212630, A212631, A212632.
Sequence in context: A086967 A098490 A247138 * A029419 A165105 A325674
Adjacent sequences: A212624 A212625 A212626 * A212628 A212629 A212630


KEYWORD

nonn,tabf


AUTHOR

Emeric Deutsch, Jun 08 2012


STATUS

approved



