Number of n X 2 0..1 arrays with each 1 horizontally or vertically adjacent to 0 or 2 1s.

Terms

a(0) =3a(1) =8a(2) =19a(3) =48a(4) =120a(5) =299a(6) =747a(7) =1865a(8) =4656a(9) =11625a(10) =29024a(11) =72464a(12) =180921a(13) =451705a(14) =1127771a(15) =2815704a(16) =7029963a(17) =17551696a(18) =43821288a(19) =109408531a(20) =273160083a(21) =681998289a(22) =1702743904a(23) =4251237649a(24) =10614057408a(25) =26500098080a(26) =66162747313a(27) =165188412465