Number of 3Xn 0..1 arrays avoiding 0 0 0 and 0 1 1 horizontally and 0 0 1 and 1 0 1 vertically.

Terms

a(0) =6a(1) =36a(2) =90a(3) =252a(4) =624a(5) =1350a(6) =3025a(7) =6256a(8) =12788a(9) =25792a(10) =50630a(11) =99012a(12) =190920a(13) =365041a(14) =694038a(15) =1309524a(16) =2460150a(17) =4599952a(18) =8565768a(19) =15899422a(20) =29415965a(21) =54278252a(22) =99908040a(23) =183482116a(24) =336298170a(25) =615243752a(26) =1123669472a(27) =2049072321a(28) =3731220822