Number of tilings of a 15 X n rectangle using 3n pentominoes of shape I.

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =1a(5) =34a(6) =95a(7) =190a(8) =325a(9) =506a(10) =3324a(11) =10353a(12) =25607a(13) =55346a(14) =108756a(15) =389216a(16) =1208901a(17) =3281686a(18) =8006108a(19) =17950204a(20) =51430928a(21) =150609259a(22) =419540401a(23) =1090827453a(24) =2651884943a(25) =7077981621a(26) =19691707908a(27) =54499735145a(28) =145671654672a(29) =371632691473