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

Terms

a(0) =19a(1) =45a(2) =115a(3) =309a(4) =859a(5) =2445a(6) =7075a(7) =20709a(8) =61099a(9) =181245a(10) =539635a(11) =1610709a(12) =4815739a(13) =14414445a(14) =43177795a(15) =129402309a(16) =387944779a(17) =1163310045a(18) =3488881555a(19) =10464547509a(20) =31389448219a(21) =94159956045a(22) =282463090915a(23) =847355718309