Number of tilings of a 12 X n rectangle using 3n tetrominoes of shape I.

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =26a(5) =75a(6) =154a(7) =269a(8) =1732a(9) =5764a(10) =15131a(11) =34345a(12) =135950a(13) =462186a(14) =1356284a(15) =3539433a(16) =11681091a(17) =38519022a(18) =118366429a(19) =334591568a(20) =1037603086a(21) =3309045401a(22) =10296063522a(23) =30414763937a(24) =92735958046a(25) =289374852696a(26) =899439481823