Number of (n+1) X 9 0..2 arrays with every 2 X 2 subblock summing to 4.

Terms

a(0) =20709a(1) =22767a(2) =26901a(3) =35223a(4) =52029a(5) =86127a(6) =155781a(7) =299463a(8) =599949a(9) =1240287a(10) =2639061a(11) =5790903a(12) =13157469a(13) =31079247a(14) =76488741a(15) =196005543a(16) =521132589a(17) =1429667007a(18) =4021576821a(19) =11529919383a(20) =33520173309a(21) =98421387567a(22) =290985935301