a(n) = Sum_{k=1..n} binomial(n,k) * sigma_2(k).

Terms

a(0) =1a(1) =7a(2) =28a(3) =95a(4) =286a(5) =802a(6) =2143a(7) =5519a(8) =13807a(9) =33762a(10) =81060a(11) =191678a(12) =447396a(13) =1032647a(14) =2360593a(15) =5351231a(16) =12041764a(17) =26920297a(18) =59829006a(19) =132262550a(20) =290990077a(21) =637429514a(22) =1390811841a(23) =3023647046a(24) =6551547161a(25) =14151910442a(26) =30481920523a(27) =65480947739a(28) =140318385088a(29) =299995596747