Product_{k>=1} (1 + x^k)^a(k) = 1 + 2x.

Terms

a(0) =2a(1) =-1a(2) =2a(3) =-4a(4) =6a(5) =-9a(6) =18a(7) =-34a(8) =56a(9) =-99a(10) =186a(11) =-344a(12) =630a(13) =-1161a(14) =2182a(15) =-4114a(16) =7710a(17) =-14532a(18) =27594a(19) =-52476a(20) =99858a(21) =-190557a(22) =364722a(23) =-699214a(24) =1342176a(25) =-2580795a(26) =4971008a(27) =-9587556a(28) =18512790a(29) =-35790267