Euler transform of sigma(n), cf. A000203.

Terms

a(0) =1a(1) =1a(2) =4a(3) =8a(4) =21a(5) =39a(6) =92a(7) =170a(8) =360a(9) =667a(10) =1316a(11) =2393a(12) =4541a(13) =8100a(14) =14824a(15) =26071a(16) =46422a(17) =80314a(18) =139978a(19) =238641a(20) =408201a(21) =686799a(22) =1156062a(23) =1920992a(24) =3189144a(25) =5238848a(26) =8589850a(27) =13963467a(28) =22641585a(29) =36447544