n-vertex sequences of plane forests with nondecreasing numbers of trees.

Terms

a(0) =1a(1) =1a(2) =3a(3) =9a(4) =29a(5) =96a(6) =326a(7) =1127a(8) =3952a(9) =14019a(10) =50208a(11) =181275a(12) =659039a(13) =2410433a(14) =8862750a(15) =32739168a(16) =121443136a(17) =452167865a(18) =1689237104a(19) =6330103627a(20) =23787215202a(21) =89616350271a(22) =338417312294