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

Terms

a(0) =1a(1) =5a(2) =16a(3) =45a(4) =116a(5) =284a(6) =673a(7) =1557a(8) =3535a(9) =7910a(10) =17502a(11) =38376a(12) =83500a(13) =180479a(14) =387881a(15) =829605a(16) =1766998a(17) =3749765a(18) =7931114a(19) =16724870a(20) =35173777a(21) =73794660a(22) =154485527a(23) =322771344a(24) =673155141a(25) =1401536934a(26) =2913490375a(27) =6047714599a(28) =12536770558a(29) =25956242579