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%I #10 Feb 14 2021 02:28:57
%S 0,4,96,4320,322560,36288000,5748019200,1220496076800,334764638208000,
%T 115242726703104000,48658040163532800000,24728016011107368960000,
%U 14890761641597746544640000,10485577989291746525184000000
%N a(n) = 2*n*(2*n)!.
%H Wikipedia, <a href="https://en.wikipedia.org/wiki/Trigonometric_integral#Cosine_integral">Cosine integral</a>.
%H Wikipedia, <a href="https://en.wikipedia.org/wiki/Trigonometric_integral#Hyperbolic_cosine_integral">Hyperbolic cosine integral</a>.
%F From _Amiram Eldar_, Feb 14 2021: (Start)
%F a(n) = A001563(2*n) = 2*n*A010050(n).
%F Sum_{n>=1} 1/a(n) = Chi(1) - gamma = A099284 - A001620, where Chi(x) is the hyperbolic cosine integral
%F Sum_{n>=1} (-1)^(n+1)/a(n) = gamma - Ci(1) = A001620 - A099282, where Ci(x) is the cosine integral. (End)
%t a[n_] := 2*n*(2*n)!; Array[a, 14, 0] (* _Amiram Eldar_, Feb 14 2021 *)
%o (PARI) for(n=0,22,print((2*n)*(2*n)!))
%Y Cf. A001563, A001620, A010050, A099282, A099284.
%K easy,nonn
%O 0,2
%A _Jason Earls_, Jul 18 2001
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