Number of (n+1) X 3 0..2 arrays with every 2 X 2 subblock summing to 4.

Terms

a(0) =45a(1) =87a(2) =189a(3) =447a(4) =1125a(5) =2967a(6) =8109a(7) =22767a(8) =65205a(9) =189447a(10) =556029a(11) =1643487a(12) =4881285a(13) =14545527a(14) =43439949a(15) =129926607a(16) =388993365a(17) =1165407207a(18) =3493075869a(19) =10472936127a(20) =31406225445a(21) =94193510487a(22) =282530199789a(23) =847489936047