G.f.: A(x) = exp( Sum_{n>=1} (1 + sigma(n)*x)^n * x^n/n ).

Terms

a(0) =1a(1) =1a(2) =2a(3) =5a(4) =14a(5) =40a(6) =154a(7) =631a(8) =2246a(9) =10476a(10) =71232a(11) =383220a(12) =1553841a(13) =8223567a(14) =58756725a(15) =338290401a(16) =1754330940a(17) =11744499990a(18) =103864469131