Near duplicate of A071277.

Terms

a(0) =2a(1) =4a(2) =8a(3) =88a(4) =252a(5) =2112a(6) =2112a(7) =2112a(8) =4224a(9) =8448a(10) =48384a(11) =48384a(12) =405504a(13) =405504a(14) =405504a(15) =40955904a(16) =677707776a(17) =677707776a(18) =677707776a(19) =677707776a(20) =677574475776a(21) =677574475776