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

Terms

a(0) =1a(1) =1a(2) =2a(3) =6a(4) =8a(5) =10a(6) =14a(7) =18a(8) =26a(9) =34a(10) =46a(11) =58a(12) =74a(13) =90a(14) =114a(15) =138a(16) =174a(17) =210a(18) =260a(19) =310a(20) =378a(21) =446a(22) =536a(23) =626a(24) =748a(25) =870a(26) =1034a(27) =1198a(28) =1410a(29) =1622