Number of tilings of a 5 X n rectangle using n pentominoes of shapes P, X, Y.

Terms

a(0) =1a(1) =0a(2) =2a(3) =4a(4) =18a(5) =36a(6) =138a(7) =334a(8) =1066a(9) =3096a(10) =9490a(11) =26826a(12) =80468a(13) =235718a(14) =699056a(15) =2055466a(16) =6074498a(17) =17857906a(18) =52725190a(19) =155445504a(20) =458505084a(21) =1351257730a(22) =3984941402a(23) =11748306100a(24) =34643781158a(25) =102144907886a(26) =301179533022a(27) =887996181502