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 A214577 The Matula-Goebel numbers of the generalized Bethe trees. A generalized Bethe tree is a rooted tree in which vertices at the same level have the same degree. 51
 2, 3, 4, 5, 7, 8, 9, 11, 16, 17, 19, 23, 25, 27, 31, 32, 49, 53, 59, 64, 67, 81, 83, 97, 103, 121, 125, 127, 128, 131, 227, 241, 243, 256, 277, 289, 311, 331, 343, 361, 419, 431, 509, 512, 529, 563, 625, 661, 691, 709, 719, 729, 739, 961, 1024, 1331, 1433, 1523, 1543, 1619, 1787, 1879, 2048, 2063, 2187, 2221, 2309, 2401, 2437, 2809, 2897 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 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. Generalized Bethe trees are called uniform trees in the Goldberg - Livshits reference. There is a simple bijection between generalized Bethe trees with n edges and partitions of n in which each part is divisible by the next (the parts are given by the number of edges at the successive levels). We have the correspondences: number of edges --- sum of parts; root degree --- last part; number of leaves --- first part; height --- number of parts. LINKS E. Deutsch, Rooted tree statistics from Matula numbers, arXiv:1111.4288 [math.CO], 2011. E. Deutsch, Rooted tree statistics from Matula numbers, Discrete Appl. Math., 160, 2012, 2314-2322. F. Goebel, On a 1-1-correspondence between rooted trees and natural numbers, J. Combin. Theory, B 29 (1980), 141-143. M. K. Goldberg and E. M. Livshits, On minimal universal trees, Mathematical Notes of the Acad. of Sciences of the USSR, 4, 1968, 713-717 (translation from the Russian Mat. Zametki 4 1968 371-379). 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. O. Rojo, Spectra of weighted generalized Bethe trees joined at the root, Linear Algebra and its Appl., 428, 2008, 2961-2979. FORMULA In A214578 one has defined Q(n)=0 if n is the Matula-Goebel number of a rooted tree that is not a generalized Bethe tree and Q(n) to be a certain polynomial if n corresponds to a generalized Bethe tree. The Maple  program makes use of this to find the Matula-Goebel numbers corresponding to the generalized Bethe trees. EXAMPLE 7 is in the sequence because the corresponding rooted tree is Y, a generalized Bethe tree. MAPLE with(numtheory): Q := 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 0 elif n = 2 then 1 elif bigomega(n) = 1 and Q(pi(n)) = 0 then 0 elif bigomega(n) = 1 then sort(expand(1+x*Q(pi(n)))) elif Q(r(n)) <> 0 and Q(s(n)) <> 0 and type(simplify(Q(r(n))/Q(s(n))), constant) = true then sort(Q(r(n))+Q(s(n))) else 0 end if end proc: A := {}; for n to 3000 do if Q(n) = 0 then  else A := `union`(A, {n}) end if end do: A; CROSSREFS Cf. A214578. Differs from A243497 for the first time at n=31. Sequence in context: A318690 A302498 A243497 * A280994 A138039 A289995 Adjacent sequences:  A214574 A214575 A214576 * A214578 A214579 A214580 KEYWORD nonn AUTHOR Emeric Deutsch, Aug 18 2012 STATUS approved

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Last modified October 22 19:53 EDT 2019. Contains 328319 sequences. (Running on oeis4.)