Partial sums of A000798.A173399Partial sums of A000798.Terms a(0) =1a(1) =2a(2) =6a(3) =35a(4) =390a(5) =7332a(6) =216859a(7) =9752100a(8) =652531454a(9) =63912820877External referencesoeis: A173399