Number of walks of length n between opposite vertices on a triangular prism.

Terms

a(0) =0a(1) =1a(2) =0a(3) =7a(4) =8a(5) =51a(6) =100a(7) =407a(8) =1008a(9) =3451a(10) =9500a(11) =30207a(12) =87208a(13) =268451a(14) =791700a(15) =2402407a(16) =7152608a(17) =21567051a(18) =64482700a(19) =193885007a(20) =580781208a(21) =1744091251a(22) =5228778500a(23) =15693326007a(24) =47065997008a(25) =141225953051a(26) =423621935100