a(n) = A091137(n+1)/(n+1).

Terms

a(0) =2a(1) =6a(2) =8a(3) =180a(4) =288a(5) =10080a(6) =17280a(7) =453600a(8) =806400a(9) =47900160a(10) =87091200a(11) =217945728000a(12) =402361344000