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A212632 The domination number of the rooted tree with Matula-Goebel number n. 15
1, 1, 1, 1, 2, 2, 1, 1, 2, 2, 2, 2, 2, 2, 2, 1, 2, 3, 1, 2, 2, 2, 3, 2, 3, 3, 3, 2, 2, 3, 2, 1, 3, 2, 2, 3, 2, 2, 3, 2, 3, 3, 2, 2, 3, 3, 3, 2, 2, 3, 2, 3, 1, 4, 3, 2, 2, 3, 2, 3, 3, 3, 3, 1, 3, 3, 2, 2, 3, 3, 2, 3, 3, 3, 3, 2, 3, 4, 2, 2, 4, 3, 3, 3, 3, 3, 3, 2 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,5
COMMENTS
The domination number of a simple graph G is the minimum cardinality of a dominating subset of G.
The Matula-Goebel number of a rooted tree can be defined in the following recursive manner: to the one-vertex tree there corresponds the number 1; to a tree T with root degree 1 there corresponds the t-th prime number, where t is the Matula-Goebel 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 Matula-Goebel numbers of the m branches of T.
LINKS
S. Alikhani and Y. H. Peng, Introduction to domination polynomial of a graph, arXiv:0905.2251 [math.CO], 2009.
É. Czabarka, L. Székely, and S. Wagner, The inverse problem for certain tree parameters, Discrete Appl. Math., 157, 2009, 3314-3319.
E. Deutsch, Rooted tree statistics from Matula numbers, arXiv:1111.4288 [math.CO], 2011.
F. Goebel, On a 1-1-correspondence between rooted trees and natural numbers, J. Combin. Theory, B 29 (1980), 141-143.
I. Gutman and A. Ivic, On Matula numbers, Discrete Math., 150, 1996, 131-142.
I. Gutman and Yeong-Nan Yeh, Deducing properties of trees from their Matula numbers, Publ. Inst. Math., 53 (67), 1993, 17-22.
D. W. Matula, A natural rooted tree enumeration by prime factorization, SIAM Rev. 10 (1968) 273.
FORMULA
In A212630 one gives the domination polynomial P(n)=P(n,x) of the rooted tree with Matula-Goebel number n. We have a(n) = least exponent in P(n,x).
EXAMPLE
a(5)=2 because the rooted tree with Matula-Goebel number 5 is the path tree R - A - B - C; {A,B} is a dominating subset and there is no dominating subset of smaller cardinality.
MAPLE
with(numtheory): P := proc (n) local r, s, A, B, C:
r := n -> op(1, factorset(n)): s := n-> n/r(n):
A := proc (n) if n = 1 then x elif bigomega(n) = 1 then x*(A(pi(n))+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:
sort(expand(A(n)+B(n))) end proc:
A212632 := n->degree(P(n))-degree(numer(subs(x = 1/x, P(n)))): seq(A212632(n), n = 1 .. 120);
MATHEMATICA
A[n_] := Which[n == 1, x, PrimeOmega[n] == 1, x*(A[PrimePi[n]] + B[PrimePi[n]] + c[PrimePi[n]]), True, A[r[n]]*A[s[n]]/x];
B[n_] := Which[n == 1, 0, PrimeOmega[n] == 1, A[PrimePi[n]], True, Expand[B[r[n]]*B[s[n]] + B[r[n]]*c[s[n]] + B[s[n]]*c[r[n]]]];
c[n_] := Which[n == 1, 1, PrimeOmega[n] == 1, B[PrimePi[n]], True, Expand[c[r[n]]*c[s[n]]]];
r[n_] := FactorInteger[n][[1, 1]];
s[n_] := n/r[n];
P[n_] := Expand[A[n] + B[n]];
a[n_] := Exponent[P[n], x] - Exponent[Numerator[P[n] /. x -> 1/x // Together], x];
Array[a, 100] (* Jean-François Alcover, Nov 14 2017, after Emeric Deutsch *)
CROSSREFS
Sequence in context: A182590 A047846 A345699 * A359477 A025885 A198337
KEYWORD
nonn
AUTHOR
Emeric Deutsch, Jun 11 2012
STATUS
approved

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Last modified March 18 22:56 EDT 2024. Contains 370952 sequences. (Running on oeis4.)