Number of Hamiltonian paths in K_3 X P_n.

Terms

a(0) =3a(1) =30a(2) =144a(3) =588a(4) =2160a(5) =7440a(6) =24576a(7) =78912a(8) =248448a(9) =771456a(10) =2371968a(11) =7241856a(12) =21998976a(13) =66586752a(14) =201025920a(15) =605781120a(16) =1823094144a(17) =5481472128a(18) =16470172032a(19) =49464779904a(20) =148508372352a(21) =445764192384