Half the number of nX3 binary arrays with each element equal to at least two neighbors.

Terms

a(0) =0a(1) =1a(2) =1a(3) =2a(4) =3a(5) =7a(6) =14a(7) =31a(8) =67a(9) =148a(10) =325a(11) =717a(12) =1580a(13) =3485a(14) =7685a(15) =16950a(16) =37383a(17) =82451a(18) =181850a(19) =401083a(20) =884615a(21) =1951080a(22) =4303241a(23) =9491097a(24) =20933272a(25) =46169785a(26) =101830665a(27) =224594602a(28) =495358987a(29) =1092548639