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A205825 a(n) = n!/ceiling(n/2)!. 3

%I #19 Feb 13 2023 02:56:43

%S 1,1,2,3,12,20,120,210,1680,3024,30240,55440,665280,1235520,17297280,

%T 32432400,518918400,980179200,17643225600,33522128640,670442572800,

%U 1279935820800,28158588057600,53970627110400,1295295050649600,2490952020480000,64764752532480000

%N a(n) = n!/ceiling(n/2)!.

%F E.g.f.: (exp(x^2)*(x+1) -1)/x. - _Sergei N. Gladkovskii_, Oct 10 2012

%F Sum_{n>=0} 1/a(n) = 3/2 + 5*exp(1/4)*sqrt(Pi)*erf(1/2)/4, where erf is the error function. - _Amiram Eldar_, Feb 13 2023

%t Table[n!/Ceiling[n/2]!,{n,0,24}]

%Y Cf. A205785, A205786.

%K nonn

%O 0,3

%A _Clark Kimberling_, Feb 01 2012

%E a(0)=1 prepended and e.g.f. edited by _Alois P. Heinz_, Sep 08 2015

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Last modified March 28 13:25 EDT 2024. Contains 371254 sequences. (Running on oeis4.)