Number of (n+1)X6 0..2 arrays with every 2x2 subblock summing to 4.

Terms

a(0) =859a(1) =1125a(2) =1675a(3) =2829a(4) =5299a(5) =10725a(6) =23035a(7) =52029a(8) =123139a(9) =304725a(10) =785995a(11) =2102829a(12) =5799379a(13) =16381125a(14) =47110555a(15) =137267229a(16) =403674019a(17) =1194767925a(18) =3551796715a(19) =10590377229a(20) =31641107059a(21) =94663273125a(22) =283469724475a(23) =849368984829