Number of tilings of a 2 X n grid with monomers, dimers, and trimers.

Terms

a(0) =1a(1) =2a(2) =7a(3) =29a(4) =109a(5) =416a(6) =1596a(7) =6105a(8) =23362a(9) =89415a(10) =342193a(11) =1309593a(12) =5011920a(13) =19180976a(14) =73406985a(15) =280933906a(16) =1075154535a(17) =4114694797a(18) =15747237101a(19) =60265824784a(20) =230641706484a(21) =882682631025