1/16 the number of (n+1) X 5 0..3 arrays with all 2 X 2 subblocks having the same four values.

Terms

a(0) =91a(1) =103a(2) =124a(3) =166a(4) =244a(5) =400a(6) =700a(7) =1300a(8) =2476a(9) =4828a(10) =9484a(11) =18796a(12) =37324a(13) =74380a(14) =148300a(15) =296140a(16) =591436a(17) =1182028a(18) =2362444a(19) =4723276a(20) =9443404a(21) =18883660a(22) =37761100a(23) =75515980a(24) =151019596a(25) =302026828a(26) =604029004a(27) =1208033356a(28) =2416017484a(29) =4831985740