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A104979
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Semidiagonal sums of triangle A104978: a(n) = Sum_{k=0..[n/2]} A104978(n-k,n-2*k).
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1
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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
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,3
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FORMULA
| 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)).
G.f. satisfies: A(x) = 1 + x*A(x)^3 + x^2*A(x)^2. [From Paul D. Hanna (pauldhanna(AT)juno.com), May 27 2010]
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PROG
| (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
| Cf. A104978.
Sequence in context: A093904 A093344 A087316 * A081052 A020074 A163071
Adjacent sequences: A104976 A104977 A104978 * A104980 A104981 A104982
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KEYWORD
| nonn
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AUTHOR
| Paul D. Hanna (pauldhanna(AT)juno.com), Mar 30 2005
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