Number of n X 2 array permutations with each element making zero or one knight moves.

Terms

a(0) =1a(1) =1a(2) =4a(3) =16a(4) =36a(5) =81a(6) =225a(7) =625a(8) =1600a(9) =4096a(10) =10816a(11) =28561a(12) =74529a(13) =194481a(14) =509796a(15) =1336336a(16) =3496900a(17) =9150625a(18) =23961025a(19) =62742241a(20) =164249856a(21) =429981696a(22) =1125736704a(23) =2947295521a(24) =7716041281a(25) =20200652641a(26) =52886200900a(27) =138458410000