Number of different possible rows (or columns) in an n X n crossword puzzle.

Terms

a(0) =0a(1) =0a(2) =1a(3) =3a(4) =6a(5) =10a(6) =16a(7) =26a(8) =43a(9) =71a(10) =116a(11) =188a(12) =304a(13) =492a(14) =797a(15) =1291a(16) =2090a(17) =3382a(18) =5472a(19) =8854a(20) =14327a(21) =23183a(22) =37512a(23) =60696a(24) =98208a(25) =158904a(26) =257113a(27) =416019a(28) =673134a(29) =1089154