Number of n X 4 binary arrays with each 1 adjacent to exactly two other 1s.

Terms

a(0) =1a(1) =4a(2) =10a(3) =27a(4) =72a(5) =179a(6) =447a(7) =1139a(8) =2912a(9) =7434a(10) =18949a(11) =48256a(12) =122905a(13) =313153a(14) =797993a(15) =2033404a(16) =5181138a(17) =13201355a(18) =33636776a(19) =85706587a(20) =218381247a(21) =556436971a(22) =1417803304a(23) =3612566114a(24) =9204828661a(25) =23453934912a(26) =59760710321a(27) =152270499073