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

Terms

a(0) =1a(1) =3a(2) =4a(3) =15a(4) =31a(5) =72a(6) =176a(7) =327a(8) =751a(9) =2063a(10) =5138a(11) =12708a(12) =30993a(13) =75386a(14) =182644a(15) =433255a(16) =1004854a(17) =2279349a(18) =5115960a(19) =11580835a(20) =26533616a(21) =62024966a(22) =149683357a(23) =373141332a(24) =957942931a(25) =2516465279a(26) =6694846987a(27) =17883365774a(28) =47644695777a(29) =125952933062