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 A198339 Irregular triangle read by rows: row n is the sequence of Matula numbers of the subtrees of the rooted tree with Matula-Goebel number n. 6
 1, 1, 1, 2, 1, 1, 1, 2, 2, 3, 1, 1, 1, 2, 2, 4, 1, 1, 1, 1, 2, 2, 2, 3, 3, 5, 1, 1, 1, 1, 2, 2, 2, 3, 4, 6, 1, 1, 1, 1, 2, 2, 2, 3, 3, 4, 7, 1, 1, 1, 1, 2, 2, 2, 4, 4, 4, 8, 1, 1, 1, 1, 1, 2, 2, 2, 2, 3, 3, 4, 6, 6, 9, 1, 1, 1, 1, 1, 2, 2, 2, 2, 3, 3, 4, 5, 6, 10 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,4 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. Number of entries in row n is A184161(n). Row n>=2 can be easily identified: its first entry is the entry 1 following the first occurrence of n-1 and its last entry is the first occurrence of n. REFERENCES 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, Rooted tree statistics from Matula numbers, arXiv:1111.4288 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. FORMULA We consider separately the subtrees that contain the root (root subtrees) and those that do not contain the root (non-root subtrees). A root subtree of a rooted tree T is a subtree of T containing the root. The Matula numbers of the root subtrees of the rooted tree with Matula-Goebel number n are described in A198338. The non-root subtrees are the following: if n=1, then there is no non-root subtree; if n = p(t) (= the t-th prime), then the non-root subtrees corresoponding to n are all the subtrees corresponding to t; if n=rs (r,s >=2), then the non-root subtrees consist of the non-root subtrees corresponding to r and those corresponding to s. The Maple program, based on this recursive procedure, yields row n (<=2000; adjustable) with the command MST(n). EXAMPLE Row 4 is [1,1,1,2,2,4] because the rooted tree with Matula-Goebel number 4 is V and its subtrees are *,*,*, |, |, and V. Triangle starts: 1; 1,1,2; 1,1,1,2,2,3; 1,1,1,2,2,4; 1,1,1,1,2,2,2,3,3,5; 1,1,1,1,2,2,2,3,4,6; MAPLE m2union := proc (x, y) sort([op(x), op(y)]) end proc: with(numtheory): MRST := 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  elif bigomega(n) = 1 then [1, seq(ithprime(mrst[pi(n)][i]), i = 1 .. nops(mrst[pi(n)]))] else [seq(seq(mrst[r(n)][i]*mrst[s(n)][j], i = 1 .. nops(mrst[r(n)])), j = 1 .. nops(mrst[s(n)]))] end if end proc: MNRST := 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 [] elif bigomega(n) = 1 then m2union(mrst[pi(n)], mnrst[pi(n)]) else m2union(mnrst[r(n)], mnrst[s(n)]) end if end proc: MST := proc (n) m2union(mrst[n], mnrst[n]) end proc: for n to 2000 do mrst[n] := MRST(n): mnrst[n] := MNRST(n): mst[n] := MST(n) end do; CROSSREFS Cf. A184161, A198338, A198341. Sequence in context: A128494 A257696 A110730 * A262561 A264990 A277315 Adjacent sequences:  A198336 A198337 A198338 * A198340 A198341 A198342 KEYWORD nonn,tabf AUTHOR Emeric Deutsch, Dec 04 2011 STATUS approved

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Last modified February 29 04:32 EST 2020. Contains 332353 sequences. (Running on oeis4.)