a(n) = 2^(1-3*n)*((2*n)!)^2/n.A372184a(n) = 2^(1-3*n)*((2*n)!)^2/n.Terms a(0) =1a(1) =9a(2) =675a(3) =198450a(4) =160744500a(5) =291751267500External referencesoeis: A372184