a(0) = a(1) = 1; a(n) = [x^n] Product_{k=1..n-1} 1/(1 - x^a(k))^a(k).

Terms

a(0) =1a(1) =1a(2) =1a(3) =4a(4) =9a(5) =14a(6) =19a(7) =24a(8) =39a(9) =63a(10) =87a(11) =111a(12) =155a(13) =235a(14) =329a(15) =423a(16) =552a(17) =771a(18) =1091a(19) =1430a(20) =1825a(21) =2400a(22) =3295a(23) =4392a(24) =5597a(25) =7117a(26) =9367a(27) =12476a(28) =16077a(29) =20182