Number of tilings of a 4 X n rectangle using T and Z tetrominoes.

Terms

a(0) =1a(1) =0a(2) =0a(3) =0a(4) =2a(5) =4a(6) =8a(7) =18a(8) =44a(9) =104a(10) =242a(11) =564a(12) =1320a(13) =3090a(14) =7228a(15) =16904a(16) =39538a(17) =92484a(18) =216328a(19) =506002a(20) =1183564a(21) =2768424a(22) =6475506a(23) =15146580a(24) =35428712a(25) =82869778a(26) =193837148a(27) =453396168a(28) =1060519538a(29) =2480615780