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

Terms

a(0) =1a(1) =1a(2) =3a(3) =5a(4) =14a(5) =20a(6) =59a(7) =83a(8) =229a(9) =350a(10) =878a(11) =1302a(12) =3479a(13) =5068a(14) =12640a(15) =19357a(16) =47547a(17) =71173a(18) =175029a(19) =262445a(20) =635297a(21) =966680a(22) =2288213a(23) =3470143a(24) =8266788a(25) =12507003a(26) =29283071a(27) =44756825a(28) =104067224a(29) =158535387