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A257540
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Irregular triangle read by rows: row n (n>=2) contains the degrees of the level 1 vertices of the rooted tree having Matula-Goebel number n; row 1: 0.
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0
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0, 1, 2, 1, 1, 2, 1, 2, 3, 1, 1, 1, 2, 2, 1, 2, 2, 1, 1, 2, 3, 1, 3, 2, 2, 1, 1, 1, 1, 2, 1, 2, 2, 4, 1, 1, 2, 2, 3, 1, 2, 3, 1, 1, 1, 2, 2, 2, 1, 3, 2, 2, 2, 1, 1, 3, 3, 1, 2, 2, 2, 1, 1, 1, 1, 1, 2, 2, 1, 2, 2, 3, 1, 1, 2, 2, 4, 1, 4, 2, 3, 1, 1
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OFFSET
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1,3
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COMMENTS
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The Matula (or 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 the number of prime divisors of n counted with multiplicity.
Sum of entries in row n = A196052(n).
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LINKS
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FORMULA
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Denoting by DL(n) the multiset of the degrees of the level 1 vertices of the rooted tree with Matula number n, we have DL(1)=[0], DL[2]=[1], DL(i-th prime) = [1+bigomega(i)], DL(rs) = DL(r) union DL(s), where bigomega(i) is the number of prime divisors of i, counted with multiplicity (A001222) and "union" is "multiset union". The Maple program is based on these recurrence equations.
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EXAMPLE
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Row 8 is 1,1,1. Indeed, the rooted tree with Matula number 8 is the star tree \|/; vertices at level 1 have degrees 1,1,1.
Triangle starts:
0;
1;
2;
1,1;
2;
1,2;
3;
1,1,1;
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MAPLE
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with(numtheory): DL := proc (n) if n = 2 then [1] elif bigomega(n) = 1 then [1+bigomega(pi(n))] else [op(DL(op(1, factorset(n)))), op(DL(n/op(1, factorset(n))))] end if end proc: with(numtheory): DL := proc (n) if n = 1 then [0] elif n = 2 then [1] elif bigomega(n) = 1 then [1+bigomega(pi(n))] else [op(DL(op(1, factorset(n)))), op(DL(n/op(1, factorset(n))))] end if end proc: seq(op(DL(n)), n = 1 .. 100);
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CROSSREFS
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KEYWORD
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nonn,tabf
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AUTHOR
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STATUS
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approved
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