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A245050
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Number of hybrid 7-ary trees with n internal nodes.
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2
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1, 2, 27, 521, 11764, 290305, 7585749, 206294771, 5778015219, 165541098701, 4828687088591, 142916854642246, 4281359716909135, 129567073833995237, 3955263087052174005, 121649279851846182073, 3766009580469162813492, 117260083892211493754415
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OFFSET
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0,2
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LINKS
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FORMULA
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a(n) = 1/(6*n+1) * Sum_{i=0..n} C(6*n+i,i)*C(6*n+i+1,n-i).
a(n) = [x^n] ((1+x)/(1-x-x^2))^(6*n+1) / (6*n+1).
G.f. satisfies: A(x) = (1+x*A(x)^6) * (1+x*A(x)^7).
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MAPLE
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a:= n-> add(binomial(6*n+i, i)*binomial(6*n+i+1, n-i), i=0..n)/(6*n+1):
seq(a(n), n=0..20);
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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