Number of Hamiltonian cycles in K_4 X P_n.

Terms

a(0) =3a(1) =30a(2) =198a(3) =1326a(4) =8886a(5) =59550a(6) =399078a(7) =2674446a(8) =17922966a(9) =120111870a(10) =804937158a(11) =5394336366a(12) =36150480246a(13) =242264688990