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 A253665 a(n) = 2^n*n!/(floor(n/2)!)^2. 3
 1, 2, 8, 48, 96, 960, 1280, 17920, 17920, 322560, 258048, 5677056, 3784704, 98402304, 56229888, 1686896640, 843448320, 28677242880, 12745441280, 484326768640, 193730707456, 8136689713152, 2958796259328, 136104627929088, 45368209309696, 2268410465484800 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 LINKS G. C. Greubel, Table of n, a(n) for n = 0..500 FORMULA a(n) = 2^n*A056040(n). a(2*n) = 4^n*C(2*n, n) = A098430(n). a(n) = sum(k=0..n, C(n,k)*n!/(floor(n/2)!)^2) = sum(k=0..n, A253666(n,k)). G.f.: (1+2*(1-8*x)*x)/(1-16*x^2)^(3/2). - Benedict W. J. Irwin, Aug 15 2016 MAPLE a := n -> 2^n*n!/iquo(n, 2)!^2: seq(a(n), n=0..25); MATHEMATICA Table[2^n*n!/Floor[n/2]!^2, {n, 0, 25}] (* Michael De Vlieger, Feb 02 2015 *) CoefficientList[Series[(1 + 2 (1 - 8 x) x)/(1 - 16 x^2)^(3/2), {x, 0, 20}], x] (* Benedict W. J. Irwin, Aug 15 2016 *) PROG (PARI) a(n)=2^n*n!/(n\2)!^2 \\ Charles R Greathouse IV, Aug 25 2016 CROSSREFS Cf. A056040, A253666, A098430. Sequence in context: A181413 A358822 A003275 * A078558 A003032 A193944 Adjacent sequences: A253662 A253663 A253664 * A253666 A253667 A253668 KEYWORD nonn AUTHOR Peter Luschny, Feb 01 2015 STATUS approved

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Last modified June 15 09:53 EDT 2024. Contains 373407 sequences. (Running on oeis4.)