Number of (undirected) paths in the ladder graph P_2 X P_n.

Terms

a(0) =1a(1) =12a(2) =49a(3) =146a(4) =373a(5) =872a(6) =1929a(7) =4118a(8) =8589a(9) =17644a(10) =35889a(11) =72538a(12) =146021a(13) =293200a(14) =587801a(15) =1177278a(16) =2356541a(17) =4715412a(18) =9433537a(19) =18870210a(20) =37744021a(21) =75492152a(22) =150988969a(23) =301983206a(24) =603972333a(25) =1207951292a(26) =2415909969a(27) =4831828138a(28) =9663665349a(29) =19327340704