Number of tilings of a 18 X n rectangle using 3n hexominoes of shape I.

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =1a(5) =1a(6) =43a(7) =117a(8) =229a(9) =385a(10) =591a(11) =853a(12) =5789a(13) =17163a(14) =40521a(15) =84211a(16) =160143a(17) =284639a(18) =945352a(19) =2743255a(20) =7017326a(21) =16250983a(22) =34801374a(23) =69959957a(24) =179843441a(25) =479965811a(26) =1238082783a(27) =3015746329a(28) =6925030997a(29) =15065972891