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Ratios of successive terms are 1,1,1,2,3,3,3,4,5,5,5,6,...
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%I #18 Jun 20 2018 01:34:32

%S 1,1,1,1,2,6,18,54,216,1080,5400,27000,162000,1134000,7938000,

%T 55566000,444528000,4000752000,36006768000,324060912000,3240609120000,

%U 35646700320000,392113703520000,4313250738720000

%N Ratios of successive terms are 1,1,1,2,3,3,3,4,5,5,5,6,...

%H Robert Israel, <a href="/A004529/b004529.txt">Table of n, a(n) for n = 0..506</a>

%F a(n) = Product_{j=0..n-1} (A180969(2,j+1) + A180969(2,j) + 1) = a(n-1) * (A180969(2,n-1) + A180969(2,n-2) + 1). - _Adriano Caroli_, Nov 27 2010

%F a(4*k+j) = 16^k * k! * Gamma(k+1/2)^3*(2*k+1)^j/Gamma(1/2)^3 for 0 <= j <= 3. - _Robert Israel_, Jun 19 2018

%p seq(seq(16^k * k! * GAMMA(k+1/2)^3*(2*k+1)^j/GAMMA(1/2)^3,j=0..3),k=0..10); # _Robert Israel_, Jun 19 2018

%K nonn

%O 0,5

%A _N. J. A. Sloane_