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 A249908 G.f. (1-x)/(2*sqrt(5*x^2 + 2*x + 1)) - 1/2. 0
 -1, 0, 3, -5, -3, 26, -35, -48, 245, -248, -639, 2355, -1573, -7890, 22555, -6685, -93075, 212280, 27625, -1061415, 1938855, 1276550, -11763465, 16906450, 23324507, -126971664, 136840575, 343314517, -1334857995, 965192298 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 LINKS FORMULA a(n) = Sum_{k=ceiling(n/2)..n} (-1)^k*binomial(k,n-k)*binomial(n-1,n-k). a(n) = (-1)^k*binomial(n-1, n-k)*binomial(k, n-k)*hypergeom([1, 1+k, -n+k, -n+k], [k, 1/2-n/2+k, 1-n/2+k], -1/4) where k = ceiling(n/2). - Peter Luschny, Nov 09 2014 D-finite with recurrence: n*a(n) + (n+1)*a(n-1) + 3*n*a(n-2) + 5*(-n+3)*a(n-3) = 0. - R. J. Mathar, May 22 2019 n*(4*n-7)*a(n) + 2*(4*n-1)*(n-2)*a(n-1) + 5*(4*n-3)*(n-2)*a(n-2) = 0. - R. J. Mathar, May 22 2019 MAPLE T := (n, k) -> (-1)^k*binomial(n-1, n-k)*binomial(k, n-k)* hypergeom([1, 1+k, -n+k, -n+k], [k, 1/2-n/2+k, 1-n/2+k], -1/4): seq(simplify(T(n, ceil(n/2))), n=1..30); # Peter Luschny, Nov 09 2014 MATHEMATICA Rest[CoefficientList[Series[(1 - x) / (2 Sqrt[5 x^2 + 2 x + 1]) - 1/2, {x, 0, 40}], x]] (* Vincenzo Librandi, Nov 08 2014 *) PROG (Maxima) a(n):=sum((-1)^k*binomial(k, n-k)*binomial(n-1, n-k), k, ceiling(n/2), n); (PARI) a(n) = sum(k=ceil(n/2), n, (-1)^k*binomial(k, n-k)*binomial(n-1, n-k)); \\ Michel Marcus, Nov 09 2014 CROSSREFS Sequence in context: A134771 A080349 A249012 * A195418 A065974 A096822 Adjacent sequences:  A249905 A249906 A249907 * A249909 A249910 A249911 KEYWORD sign AUTHOR Vladimir Kruchinin, Nov 08 2014 STATUS approved

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Last modified April 21 19:16 EDT 2021. Contains 343156 sequences. (Running on oeis4.)