Number of (undirected) cycles on the n X 2 king graph.

Terms

a(0) =7a(1) =30a(2) =85a(3) =204a(4) =451a(5) =954a(6) =1969a(7) =4008a(8) =8095a(9) =16278a(10) =32653a(11) =65412a(12) =130939a(13) =262002a(14) =524137a(15) =1048416a(16) =2096983a(17) =4194126a(18) =8388421a(19) =16777020a(20) =33554227a(21) =67108650a(22) =134217505a(23) =268435224a(24) =536870671a(25) =1073741574a(26) =2147483389a(27) =4294967028a(28) =8589934315a(29) =17179868898