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 A182907 Triangle read by rows: row n is the degree sequence (written in nondecreasing order) of the rooted tree with Matula-Goebel number n. 6
 0, 1, 1, 1, 1, 2, 1, 1, 2, 1, 1, 2, 2, 1, 1, 2, 2, 1, 1, 1, 3, 1, 1, 1, 3, 1, 1, 2, 2, 2, 1, 1, 2, 2, 2, 1, 1, 2, 2, 2, 1, 1, 1, 2, 3, 1, 1, 1, 2, 3, 1, 1, 1, 2, 3, 1, 1, 2, 2, 2, 2, 1, 1, 1, 1, 4, 1, 1, 1, 2, 3, 1, 1, 1, 2, 2, 3, 1, 1, 1, 1, 4, 1, 1, 1, 2, 2, 3, 1, 1, 1, 2, 2, 3, 1, 1, 2, 2, 2, 2, 1, 1, 1, 2, 2, 3, 1, 1, 1, 1, 2, 4, 1, 1, 2, 2, 2, 2, 2 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,6 COMMENTS 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. The number of entries in row n is A061775(n) (= number of vertices of the rooted tree). REFERENCES 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 Review, 10, 1968, 273. LINKS E. Deutsch, Tree statistics from Matula numbers, arXiv preprint arXiv:1111.4288, 2011 FORMULA For a graph with degree sequence a,b,c,..., define the degree sequence polynomial to be x^a + x^b + x^c + ... . The degree sequence polynomial g(n)=g(n,x) of the rooted tree with Matula-Goebel number n can be obtained recursively in the following way: g(1)=1; if n=p(t) (=the t-th prime), then g(n)=g(t)+x^G(t)*(x-1)+x; if n=rs (r,s>=2), then g(n)=g(r)+g(s)-x^G(r)-x^G(s)+x^G(n); G(m) is the number of prime divisors of m counted with multiplicities. The Maple program, based on this recursive procedure, finds for an arbitrary n the polynomial g(n,x) and then extracts from this polynomial the degree sequence S(n). EXAMPLE Row 7 is 1,1,1,3 because the rooted tree with Matula-Goebel number 7 is the rooted tree Y. Row 32 is 1,1,1,1,1,5 because the rooted tree with Matula-Goebel number 32 is a star with 5 edges. MAPLE with(numtheory): g := 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(g(pi(n))+x^bigomega(pi(n))*(x-1)+x)) else sort(expand(g(r(n))+g(s(n))-x^bigomega(r(n))-x^bigomega(s(n))+x^bigomega(n))) end if end proc: S := proc (n) if n = 1 then 0 else seq(seq(j, i = 1 .. coeff(g(n), x, j)), j = 1 .. degree(g(n))) end if end proc: for n to 25 do S(n) end do; # yields sequence in triangular form CROSSREFS Sequence in context: A050412 A307017 A220424 * A334745 A323231 A175128 Adjacent sequences:  A182904 A182905 A182906 * A182908 A182909 A182910 KEYWORD nonn,tabf AUTHOR Emeric Deutsch, Oct 05 2011 STATUS approved

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Last modified June 17 00:17 EDT 2021. Contains 345080 sequences. (Running on oeis4.)