Diagonal of A081957.

Terms

a(0) =2a(1) =8a(2) =36a(3) =180a(4) =1080a(5) =7560a(6) =60480a(7) =524160a(8) =5241600a(9) =56609280a(10) =670602240a(11) =8622028800a(12) =118879488000