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 A196066 The reverse Wiener index of the rooted tree with Matula-Goebel number n. 0
 0, 0, 2, 2, 8, 8, 3, 3, 20, 20, 20, 12, 12, 12, 40, 4, 12, 29, 4, 28, 28, 40, 29, 17, 70, 29, 36, 16, 28, 55, 40, 5, 70, 28, 53, 40, 17, 17, 55, 38, 29, 38, 16, 53, 68, 36, 55, 23, 36, 93, 53, 38, 5, 48, 112, 21, 38, 55, 28, 73, 40, 70, 45, 6, 92, 92, 17, 36, 68, 70, 38, 53, 38, 40, 114, 21, 89, 72, 53, 50 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS The reverse Wiener index of a connected graph is (1/2)N(N-1)D - W, where N, D, and W are, respectively, the number of vertices, the diameter, and the Wiener index of the graph. The Matula-Goebel number of a rooted tree is 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. 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. A. T. Balaban, D. Mills, O. Ivanciuc, and S. C. Basak, Reverse Wiener indices, Croatica Chemica Acta, 73 (4), 2000, 923-941. LINKS FORMULA a(n)=(1/2)N(n)*(N(n)-1)*d(n) - W(n),  where N, d, and W are, respectively, the number of vertices, the diameter, and the Wiener index of the rooted tree with Matula-Goebel number n  (all these data are contained in the Wiener polynomial; see A196059). The Maple program is based on the above. EXAMPLE a(7)=3 because the rooted tree with Matula-Goebel number 7 is the rooted tree Y with N=4, d=2, W=9 (distances are 1,1,1,2,2,2); (1/2)*4*3*2-9 = 3. MAPLE with(numtheory): Wp := proc (n) local r, s, R: r := proc (n) options operator, arrow: op(1, factorset(n)) end proc: s := proc (n) options operator, arrow: n/r(n) end proc: R := proc (n) if n = 1 then 0 elif bigomega(n) = 1 then sort(expand(x*R(pi(n))+x)) else sort(expand(R(r(n))+R(s(n)))) end if end proc: if n = 1 then 0 elif bigomega(n) = 1 then sort(expand(Wp(pi(n))+x*R(pi(n))+x)) else sort(expand(Wp(r(n))+Wp(s(n))+R(r(n))*R(s(n)))) end if end proc: N := proc (n) options operator, arrow: 1+coeff(Wp(n), x) end proc: d := proc (n) options operator, arrow: degree(Wp(n)) end proc: W := proc (n) options operator, arrow: subs(x = 1, diff(Wp(n), x)) end proc: a := proc (n) options operator, arrow: (1/2)*N(n)*(N(n)-1)*d(n)-W(n) end proc: 0, seq(a(n), n = 2 .. 80); CROSSREFS Cf. A196059. Sequence in context: A195138 A094887 A021441 * A334574 A260825 A330763 Adjacent sequences:  A196063 A196064 A196065 * A196067 A196068 A196069 KEYWORD nonn AUTHOR Emeric Deutsch, Oct 01 2011 STATUS approved

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Last modified September 20 16:31 EDT 2020. Contains 337265 sequences. (Running on oeis4.)