L.g.f.: Sum_{n>=1} (x^n/n) / Product_{d|n} (1 - n*x^d/d).

Terms

a(0) =1a(1) =3a(2) =7a(3) =19a(4) =51a(5) =159a(6) =519a(7) =1867a(8) =7234a(9) =30243a(10) =135125a(11) =642307a(12) =3231047a(13) =17138845a(14) =95554662a(15) =558384955a(16) =3411049542a(17) =21730279218a(18) =144048688538a(19) =991665854999