G.f.: Sum_{n>=0} x^n * Product_{k=1..n} (1+x^k)/(1-x^k).

Terms

a(0) =1a(1) =1a(2) =3a(3) =5a(4) =9a(5) =15a(6) =25a(7) =39a(8) =61a(9) =93a(10) =139a(11) =205a(12) =299a(13) =429a(14) =611a(15) =861a(16) =1201a(17) =1663a(18) =2285a(19) =3115a(20) =4221a(21) =5683a(22) =7605a(23) =10123a(24) =13405a(25) =17661a(26) =23163a(27) =30245a(28) =39323a(29) =50925