Number of closed Knight's tours on a 3 X n board.

Terms

a(0) =0a(1) =0a(2) =0a(3) =0a(4) =0a(5) =0a(6) =0a(7) =0a(8) =0a(9) =16a(10) =0a(11) =176a(12) =0a(13) =1536a(14) =0a(15) =15424a(16) =0a(17) =147728a(18) =0a(19) =1448416a(20) =0a(21) =14060048a(22) =0a(23) =136947616a(24) =0a(25) =1332257856a(26) =0a(27) =12965578752a(28) =0a(29) =126169362176