Number of nX4 0..1 arrays with each 1 horizontally or vertically adjacent to 2 or 4 1s.

Terms

a(0) =1a(1) =4a(2) =14a(3) =42a(4) =108a(5) =284a(6) =777a(7) =2146a(8) =5887a(9) =16061a(10) =43813a(11) =119691a(12) =327167a(13) =894141a(14) =2443118a(15) =6675212a(16) =18239201a(17) =49837854a(18) =136179673a(19) =372101538a(20) =1016738643a(21) =2778163068a(22) =7591134970a(23) =20742245392a(24) =56676717731a(25) =154865094839a(26) =423157850846