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A245051
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Number of hybrid 8-ary trees with n internal nodes.
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2
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1, 2, 31, 691, 18054, 515892, 15615159, 492007235, 15968172965, 530169356965, 17922457144129, 614796956579459, 21346411113410148, 748762981653051898, 26493592534823331169, 944491728494004127029, 33892155096781949014406, 1223212951343094980654244
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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/(7*n+1) * Sum_{i=0..n} C(7*n+i,i)*C(7*n+i+1,n-i).
a(n) = [x^n] ((1+x)/(1-x-x^2))^(7*n+1) / (7*n+1).
G.f. satisfies: A(x) = (1+x*A(x)^7) * (1+x*A(x)^8).
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MAPLE
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a:= n-> add(binomial(7*n+i, i)*binomial(7*n+i+1, n-i), i=0..n)/(7*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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