a(n) = sigma(n*2^(n-1)).

Terms

a(0) =1a(1) =7a(2) =28a(3) =63a(4) =186a(5) =508a(6) =1016a(7) =2047a(8) =6643a(9) =12282a(10) =24564a(11) =65532a(12) =114674a(13) =262136a(14) =786408a(15) =1048575a(16) =2359278a(17) =6815731a(18) =10485740a(19) =25165818a(20) =67108832a(21) =100663284a(22) =201326568a(23) =536870908a(24) =1040187361a(25) =1879048178a(26) =5368709080a(27) =8589934584