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Search: id:A104979
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| 1, 1, 4, 17, 85, 459, 2614, 15454, 93947, 583568, 3687761, 23633072, 153227250, 1003281314, 6624658716, 44062205158, 294938814921, 1985330061570, 13430612284606, 91262392343333, 622624395706714, 4263163419492661
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OFFSET
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0,3
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FORMULA
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a(n) = Sum_{k=0..[n/2]} C(3*n-4*k, 3*n-5*k)*C(3*n-5*k, n-2*k)/(2*n-3*k+1)).
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PROGRAM
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(PARI) {a(n)=sum(k=0, n\2, binomial(3*n-4*k, 3*n-5*k)*binomial(3*n-5*k, n-2*k)/(2*n-3*k+1))}
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CROSSREFS
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Cf. A104978.
Sequence in context: A093344 A087316 A113171 this_sequence A081052 A020074 A056542
Adjacent sequences: A104976 A104977 A104978 this_sequence A104980 A104981 A104982
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KEYWORD
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nonn
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AUTHOR
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Paul D. Hanna (pauldhanna(AT)juno.com), Mar 30 2005
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