Number of incongruent domino tilings of the 3 X (2n) board.

Terms

a(0) =1a(1) =2a(2) =5a(3) =14a(4) =46a(5) =156a(6) =561a(7) =2037a(8) =7525a(9) =27874a(10) =103741a(11) =386386a(12) =1440946a(13) =5374772a(14) =20054945a(15) =74835209a(16) =279273961a(17) =1042224066a(18) =3889577781a(19) =14515950582a(20) =54174058390a(21) =202179773644a(22) =754544416081