a(n) = Product_{k=1..n} (2*k-1)^(2*n-2*k+1).A136411a(n) = Product_{k=1..n} (2*k-1)^(2*n-2*k+1).Terms a(0) =1a(1) =3a(2) =135a(3) =212625a(4) =21097715625External referencesoeis: A136411