The number of tight 3 X n pavings.

Terms

a(0) =0a(1) =1a(2) =11a(3) =64a(4) =282a(5) =1071a(6) =3729a(7) =12310a(8) =39296a(9) =122773a(10) =378279a(11) =1154988a(12) =3505542a(13) =10598107a(14) =31957661a(15) =96200098a(16) =289255020a(17) =869075073a(18) =2609845875a(19) =7834779640a(20) =23514823730a(21) =70565441671a(22) =211738266921a(23) =635298685614