Number of tilings of a 2 X n rectangle using pentominoes of any shape and monominoes.

Terms

a(0) =1a(1) =1a(2) =1a(3) =7a(4) =25a(5) =50a(6) =155a(7) =508a(8) =1343a(9) =3800a(10) =11438a(11) =32525a(12) =92333a(13) =268766a(14) =774302a(15) =2216976a(16) =6392865a(17) =18425916a(18) =52958070a(19) =152425812a(20) =438973764a(21) =1263109849a(22) =3634965137a(23) =10463959311a(24) =30116734921a(25) =86675829307a(26) =249478723992a(27) =718056248229