Number of Hamiltonian cycles in C_4 X P_n.

Terms

a(0) =1a(1) =6a(2) =22a(3) =82a(4) =306a(5) =1142a(6) =4262a(7) =15906a(8) =59362a(9) =221542a(10) =826806a(11) =3085682a(12) =11515922a(13) =42978006a(14) =160396102a(15) =598606402a(16) =2234029506a(17) =8337511622a(18) =31116016982a(19) =116126556306a(20) =433390208242