(2*n)!*((2*n+1)/2)^n/(2*n+1).A216728(2*n)!*((2*n+1)/2)^n/(2*n+1).Terms a(0) =1a(1) =1a(2) =30a(3) =4410a(4) =1837080a(5) =1660289400External referencesoeis: A216728