Product_{n>=1} (1 + a(n)*x^n) = 1 + Sum_{n>=1} sigma(n)*x^n, where sigma = A000203.

Terms

a(0) =1a(1) =3a(2) =1a(3) =6a(4) =-3a(5) =-6a(6) =-1a(7) =40a(8) =3a(9) =-50a(10) =-1a(11) =73a(12) =3a(13) =-315a(14) =1a(15) =1953a(16) =1a(17) =-2117a(18) =7a(19) =5625a(20) =-13a(21) =-16116a(22) =27a(23) =33728a(24) =29a(25) =-122648a(26) =3a(27) =351244a(28) =-25a(29) =-913057