Number of n X 2 0..1 arrays with every one equal to some NW, E or S neighbor.

Terms

a(0) =1a(1) =4a(2) =14a(3) =40a(4) =116a(5) =344a(6) =1016a(7) =2992a(8) =8816a(9) =25984a(10) =76576a(11) =225664a(12) =665024a(13) =1959808a(14) =5775488a(15) =17020160a(16) =50157824a(17) =147813376a(18) =435600896a(19) =1283700736a(20) =3783021568a(21) =11148433408a(22) =32854046720a(23) =96819736576a(24) =285324406784a(25) =840841134080