1/9 the number of (n+1) X 5 0..2 arrays with all 2 X 2 subblocks having the same four values.

Terms

a(0) =45a(1) =51a(2) =61a(3) =81a(4) =117a(5) =189a(6) =325a(7) =597a(8) =1125a(9) =2181a(10) =4261a(11) =8421a(12) =16677a(13) =33189a(14) =66085a(15) =131877a(16) =263205a(17) =525861a(18) =1050661a(19) =2100261a(20) =4198437a(21) =8394789a(22) =16785445a(23) =33566757a(24) =67125285a(25) =134242341a(26) =268468261a(27) =536920101a(28) =1073807397a(29) =2147581989