Number of tilings of a 5 X n rectangle using n pentominoes of shapes W, I, L, F.

Terms

a(0) =1a(1) =1a(2) =3a(3) =5a(4) =21a(5) =82a(6) =249a(7) =688a(8) =1879a(9) =5690a(10) =17932a(11) =55271a(12) =164427a(13) =485348a(14) =1451110a(15) =4395114a(16) =13313135a(17) =40073992a(18) =120200822a(19) =360897368a(20) =1086543152a(21) =3274191643a(22) =9858847241a(23) =29657925485a(24) =89206237151a(25) =268435863317a(26) =808022052324