a(n) = Fibonacci(n) - 3. Number of total preorders.

Terms

a(0) =0a(1) =2a(2) =5a(3) =10a(4) =18a(5) =31a(6) =52a(7) =86a(8) =141a(9) =230a(10) =374a(11) =607a(12) =984a(13) =1594a(14) =2581a(15) =4178a(16) =6762a(17) =10943a(18) =17708a(19) =28654a(20) =46365a(21) =75022a(22) =121390a(23) =196415a(24) =317808a(25) =514226a(26) =832037a(27) =1346266a(28) =2178306a(29) =3524575