Partial sums of A006384.

Terms

a(0) =1a(1) =3a(2) =7a(3) =21a(4) =78a(5) =390a(6) =2461a(7) =17491a(8) =135226a(9) =1103076a(10) =9371892a(11) =82205622a(12) =740254762a(13) =6814312822a(14) =63920746639a(15) =609452784251