a(n) = (n-1)! * Product_{i=1..n-1} ((2*n)!-2*i-1).A033636a(n) = (n-1)! * Product_{i=1..n-1} ((2*n)!-2*i-1).Terms a(0) =1a(1) =21a(2) =1025310External referencesoeis: A033636