Number of (n+1) X 3 0..2 arrays with all 2 X 2 subblock sums the same.

Terms

a(0) =171a(1) =309a(2) =579a(3) =1233a(4) =2691a(5) =6417a(6) =15555a(7) =40041a(8) =104211a(9) =282609a(10) =771699a(11) =2167353a(12) =6111171a(13) =17563617a(14) =50584035a(15) =147570921a(16) =430968051a(17) =1269505809a(18) =3741492819a(19) =11090690073a(20) =32883337251a(21) =97873303617a(22) =291340216515a(23) =869463485001