G.f.: Sum_{k>=0} (1 + k*x)^k * x^k.

Terms

a(0) =1a(1) =1a(2) =2a(3) =5a(4) =14a(5) =44a(6) =149a(7) =543a(8) =2096a(9) =8539a(10) =36444a(11) =162380a(12) =752181a(13) =3612037a(14) =17933038a(15) =91843329a(16) =484280386a(17) =2624400428a(18) =14595111277a(19) =83178971707a(20) =485218783724