Partial sums of A005001.

Terms

a(0) =1a(1) =3a(2) =7a(3) =16a(4) =40a(5) =116a(6) =395a(7) =1551a(8) =6847a(9) =33290a(10) =175708a(11) =996696a(12) =6031281a(13) =38710303a(14) =262288647a(15) =1868825536a(16) =13955504572a(17) =108907053412a(18) =885935408411