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

Terms

a(0) =81a(1) =171a(2) =361a(3) =855a(4) =2025a(5) =5175a(6) =13225a(7) =35535a(8) =95481a(9) =265431a(10) =737881a(11) =2100255a(12) =5978025a(13) =17298375a(14) =50055625a(15) =146516175a(16) =428862681a(17) =1265299191a(18) =3733087801a(19) =11073888255a(20) =32849750025a(21) =97806145575a(22) =291205933225a(23) =869194951215