Expansion of Product_{k>=1} (1 + x^k)^(sigma_2(k)).

Terms

a(0) =1a(1) =1a(2) =5a(3) =15a(4) =41a(5) =107a(6) =286a(7) =700a(8) =1735a(9) =4162a(10) =9803a(11) =22673a(12) =51822a(13) =116376a(14) =258548a(15) =567197a(16) =1230763a(17) =2642958a(18) =5622616a(19) =11850537a(20) =24769248a(21) =51353095a(22) =105662389a(23) =215838649a(24) =437890022a(25) =882562763a(26) =1767741732a(27) =3519599996a(28) =6967592060a(29) =13717874719