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A202853
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Triangle read by rows: T(n,k) is the number of k-matchings of the rooted tree having Matula-Goebel number n (n>=1, k>=0).
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5
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1, 1, 1, 1, 2, 1, 2, 1, 3, 1, 1, 3, 1, 1, 3, 1, 3, 1, 4, 3, 1, 4, 3, 1, 4, 3, 1, 4, 2, 1, 4, 2, 1, 4, 2, 1, 5, 6, 1, 1, 4, 1, 4, 2, 1, 5, 5, 1, 1, 4, 1, 5, 5, 1, 5, 5, 1, 5, 6, 1, 1, 5, 5, 1, 1, 5, 3, 1, 6, 10, 4, 1, 5, 5, 1, 1, 6, 9, 4, 1, 5, 4, 1, 5, 5, 1, 6, 9, 3, 1, 5, 6, 1, 1, 5, 1, 6, 10, 4, 1, 5, 5, 1, 6, 9, 2
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OFFSET
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1,5
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COMMENTS
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The entries in row n are the coefficients of the matching-generating polynomial of the rooted tree having Matula-Goebel number n (see the MathWorld link).
A k-matching in a graph is a set of k edges, no two of which have a vertex in common.
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.
After activating the Maple program, the command m(n) will yield the matching-generating polynomial of the rooted tree corresponding to the Matula-Goebel number n.
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REFERENCES
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C. D. Godsil, Algebraic Combinatorics, Chapman & Hall, New York, 1993.
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LINKS
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FORMULA
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Define b(n) (c(n)) to be the generating polynomials of the matchings of the rooted tree with Matula-Goebel number n that contain (do not contain) the root, with respect to the size of the matching (a k-matching has size k). We have the following recurrence for the pair M(n)=[b(n),c(n)]. M(1)=[0,1]; if n=p(t) (=the t-th prime), then M(n)=[xc(t),b(t)+c(t)]; if n=rs (r,s,>=2), then M(n)=[b(r)c(s)+c(r)b(s), c(r)c(s)]. Then m(n)=b(n)+c(n) is the generating polynomial of the matchings of the rooted tree with respect to the size of the matchings (called the matching-generating polynomial). T(n,k) is the coefficient of x^k in the polynomial m(n). [The actual matching polynomial is obtained by the substitution x = -1/x^2, followed by multiplication by x^N(n), where N(n) is the number of vertices of the rooted tree.]
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EXAMPLE
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T(11,2)=3 because the rooted tree corresponding to n=11 is a path abcde on 5 vertices. We have three 2-matchings: (ab,cd), (ab,de), and (bc,de).
Triangle starts:
1;
1,1;
1,2;
1,2;
1,3,1;
1,3,1;
...
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MAPLE
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with(numtheory): N := 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 1+N(pi(n)) else N(r(n))+N(s(n))-1 end if end proc: M := 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, 1] elif bigomega(n) = 1 then [x*M(pi(n))[2], M(pi(n))[1]+M(pi(n))[2]] else [M(r(n))[1]*M(s(n))[2]+M(r(n))[2]*M(s(n))[1], M(r(n))[2]*M(s(n))[2]] end if end proc: m := proc (n) options operator, arrow: sort(expand(M(n)[1]+M(n)[2])) end proc: for n to 35 do seq(coeff(m(n), x, j), j = 0 .. degree(m(n))) end do; # yields sequence in triangular form
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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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