From the game of Mousetrap.

Terms

a(0) =2a(1) =11a(2) =50a(3) =348a(4) =2712a(5) =23520a(6) =225360a(7) =2368800a(8) =27135360a(9) =336752640a(10) =4503340800a(11) =64585382400a(12) =989138304000