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 A104979 Semidiagonal sums of triangle A104978: a(n) = Sum_{k=0..[n/2]} A104978(n-k,n-2*k). 1
 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; text; internal format)
 OFFSET 0,3 LINKS 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, May 27 2010] 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))} CROSSREFS Cf. A104978. Sequence in context: A093904 A093344 A087316 * A081052 A020074 A163071 Adjacent sequences:  A104976 A104977 A104978 * A104980 A104981 A104982 KEYWORD nonn AUTHOR Paul D. Hanna, Mar 30 2005 STATUS approved

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Last modified October 21 08:16 EDT 2019. Contains 328292 sequences. (Running on oeis4.)