Number of cycles in the grid graph P_4 X P_{n+1}.

Terms

a(0) =6a(1) =40a(2) =213a(3) =1049a(4) =5034a(5) =23984a(6) =114069a(7) =542295a(8) =2577870a(9) =12253948a(10) =58249011a(11) =276885683a(12) =1316170990a(13) =6256394122a(14) =29739651711a(15) =141366874247a(16) =671984773580