Partial sums of A001168.

Terms

a(0) =1a(1) =3a(2) =9a(3) =28a(4) =91a(5) =307a(6) =1067a(7) =3792a(8) =13702a(9) =50148a(10) =185416a(11) =691277a(12) =2595167a(13) =9800041a(14) =37194707a(15) =141787644a(16) =542583488a(17) =2083404030a(18) =8024142706a(19) =30988922366a(20) =119972435149a(21) =465505007827