G.f.: Sum_{n>=0} x^n * (1+x)^sigma(n).

Terms

a(0) =1a(1) =1a(2) =2a(3) =4a(4) =8a(5) =15a(6) =32a(7) =64a(8) =130a(9) =300a(10) =683a(11) =1416a(12) =2797a(13) =5449a(14) =10468a(15) =20827a(16) =48713a(17) =140665a(18) =440145a(19) =1295627a(20) =3366191a(21) =7604954a(22) =15054413a(23) =26767480a(24) =45010160a(25) =78418102a(26) =156829013a(27) =367706520a(28) =935824230a(29) =2377653059