Partial sums of A004123.

Terms

a(0) =1a(1) =3a(2) =13a(3) =87a(4) =817a(5) =9819a(6) =143029a(7) =2442783a(8) =47817913a(9) =1054997475a(10) =25895101885a(11) =699790692519