Number of (undirected) Hamiltonian paths in the 2 X n king graph.

Terms

a(0) =1a(1) =12a(2) =48a(3) =208a(4) =768a(5) =2752a(6) =9472a(7) =32000a(8) =106496a(9) =351232a(10) =1150976a(11) =3756032a(12) =12222464a(13) =39698432a(14) =128778240a(15) =417398784a(16) =1352138752a(17) =4378591232a(18) =14175698944a(19) =45886734336a(20) =148520304640a(21) =480679821312