Number of Hamiltonian cycles in D_4 X P_n.

Terms

a(0) =0a(1) =2a(2) =6a(3) =24a(4) =86a(5) =320a(6) =1176a(7) =4340a(8) =15994a(9) =58970a(10) =217388a(11) =801426a(12) =2954496a(13) =10891960a(14) =40153904a(15) =148030026a(16) =545722366a(17) =2011841328a(18) =7416784934a(19) =27342464080a(20) =100799786752a(21) =371605023956