Number of Hamiltonian cycles in C_3 X C_n.

Terms

a(0) =48a(1) =126a(2) =390a(3) =1014a(4) =2982a(5) =8094a(6) =23646a(7) =66726a(8) =196086a(9) =568302a(10) =1682382a(11) =4954998a(12) =14750310a(13) =43833150a(14) =130942398a(15) =390959430a(16) =1170256854a(17) =3502513038a(18) =10495480494a(19) =31450265622a(20) =94296270918a(21) =282731526366