Number of nX3 0..1 arrays with each 1 horizontally or vertically adjacent to 2 or 4 1s.

Terms

a(0) =1a(1) =3a(2) =8a(3) =14a(4) =25a(5) =53a(6) =111a(7) =217a(8) =426a(9) =860a(10) =1733a(11) =3453a(12) =6885a(13) =13791a(14) =27616a(15) =55198a(16) =110341a(17) =220737a(18) =441563a(19) =883037a(20) =1765930a(21) =3532004a(22) =7064241a(23) =14128249a(24) =28256121a(25) =56512619a(26) =113025848a(27) =226051086a(28) =452101185a(29) =904203357