a(n) = A004125(2^n) = A004125(2^n-1).

Terms

a(0) =0a(1) =1a(2) =8a(3) =36a(4) =167a(5) =693a(6) =2849a(7) =11459a(8) =46244a(9) =185622a(10) =743759a(11) =2974937a(12) =11907026a(13) =47643438a(14) =190606963a(15) =762449101a(16) =3049917900a(17) =12199777048a(18) =48799551822a(19) =195198666492a(20) =780796575104