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A110468 a(n) = (2*n + 1)!/(n + 1).

%I A110468 #55 Jul 24 2025 07:49:34
%S A110468 1,3,40,1260,72576,6652800,889574400,163459296000,39520825344000,
%T A110468 12164510040883200,4644631106519040000,2154334728240414720000,
%U A110468 1193170003333152768000000,777776389315596582912000000,589450799582646796969574400000,513927415886120176107847680000000
%N A110468 a(n) = (2*n + 1)!/(n + 1).
%C A110468 Convolution of (-1)^n*n! and n! with interpolated zeros suppressed.
%C A110468 Denominator of absolute value of coefficient of 1/(x+n^2) in the partial fraction decomposition of 1/(x+1)*1/(x+4)*..*1/(x+n^2). - Joris Roos (jorisr(AT)gmx.de), Aug 07 2009
%C A110468 With offset = 1: a(n) is the number of permutations of {1,2,...,2n} composed of two cycles of length n. - _Geoffrey Critzer_, Nov 11 2012
%H A110468 Alois P. Heinz, <a href="/A110468/b110468.txt">Table of n, a(n) for n = 0..200</a>
%F A110468 E.g.f.: log((1-x)*(1+x))/(-x).
%F A110468 a(n) = (2*n)!*Sum_{k = 0..2*n} (-1)^k/binomial(2*n, k).
%F A110468 a(n) = Sum_{k = 0..2*n} k!*(-1)^k*(2*n-k)!.
%F A110468 Sum_{n>=0} 1/a(n) = e/2. - _Franz Vrabec_, Jan 17 2008
%F A110468 (n+1)*a(n) + 2*(-n^2)*(2*n+1)*a(n-1) = 0. - _R. J. Mathar_, Nov 15 2012
%F A110468 a(n) = Product_{i=1..n} (n+1-i)*(n+1+i). - _Vaclav Kotesovec_, Oct 21 2014
%F A110468 a(n) = A145877(2*n+2, n+1). - _Alois P. Heinz_, Apr 21 2017
%F A110468 a(n) = A346085(2*n+2, n+1). - _Alois P. Heinz_, Jul 04 2021
%F A110468 Sum_{n>=0} (-1)^n/a(n) = (cos(1) + sin(1))/2 = (1/2) * A143623. - _Amiram Eldar_, Feb 08 2022
%F A110468 a(p-1) == 1 (mod p), p a prime. - _Peter Bala_, Jul 29 2024
%F A110468 Sum_{n>=0} x^(2*n+1)/a(n) = (sinh(x) + x*cosh(x))/2. - _Michael Somos_, Jul 23 2025
%t A110468 Table[(2n)!/(2n^2),{n,1,20}] (* _Geoffrey Critzer_, Nov 11 2012 *)
%o A110468 (PARI) for(n=0,50, print1((2*n+1)!/(n+1), ", ")) \\ _G. C. Greubel_, Aug 28 2017
%Y A110468 Cf. A094310, A143623, A145877, A202768, A346085.
%K A110468 easy,nonn
%O A110468 0,2
%A A110468 _Paul Barry_, Jul 21 2005
%E A110468 Simpler definition from _Robert Israel_, Jul 20 2006