Number of Hamiltonian cycles in P_4 X P_n.

Terms

a(0) =0a(1) =1a(2) =2a(3) =6a(4) =14a(5) =37a(6) =92a(7) =236a(8) =596a(9) =1517a(10) =3846a(11) =9770a(12) =24794a(13) =62953a(14) =159800a(15) =405688a(16) =1029864a(17) =2614457a(18) =6637066a(19) =16849006a(20) =42773094a(21) =108584525a(22) =275654292a(23) =699780452a(24) =1776473532a(25) =4509783909a(26) =11448608270a(27) =29063617746a(28) =73781357746a(29) =187302518353