G.f. satisfies: A(x) = exp( Sum_{n>=1} sigma(n)*A(x^n)*x^n/n ).

Terms

a(0) =1a(1) =1a(2) =3a(3) =7a(4) =19a(5) =47a(6) =131a(7) =351a(8) =992a(9) =2808a(10) =8131a(11) =23723a(12) =70192a(13) =209209a(14) =629165a(15) =1904391a(16) =5801109a(17) =17764063a(18) =54663309a(19) =168925259a(20) =524064687a(21) =1631511342a(22) =5095440198a(23) =15960070908a(24) =50124189982a(25) =157806721089a(26) =497953049736