Number of n step self-avoiding walks on 3 X infinity grid starting from (0,0).

Terms

a(0) =1a(1) =3a(2) =7a(3) =18a(4) =40a(5) =86a(6) =170a(7) =350a(8) =688a(9) =1394a(10) =2702a(11) =5338a(12) =10278a(13) =20078a(14) =38578a(15) =74820a(16) =143496a(17) =276890a(18) =530626a(19) =1020774a(20) =1955400a(21) =3754560a(22) =7190520a(23) =13790666a(24) =26407852a(25) =50612412a(26) =96911566a(27) =185660272a(28) =355485362a(29) =680860212