Trails of length n on cubic lattice.

Terms

a(0) =1a(1) =6a(2) =30a(3) =150a(4) =750a(5) =3726a(6) =18438a(7) =90966a(8) =447918a(9) =2201622a(10) =10809006a(11) =52999446a(12) =259668942a(13) =1271054982a(14) =6218232414a(15) =30399142614