a(n) = sum(d divides n, 2^(n/d-1) - 1 ), omitting d=1 and d=n.

Terms

a(0) =0a(1) =0a(2) =0a(3) =1a(4) =0a(5) =4a(6) =0a(7) =8a(8) =3a(9) =16a(10) =0a(11) =42a(12) =0a(13) =64a(14) =18a(15) =135a(16) =0a(17) =290a(18) =0a(19) =534a(20) =66a(21) =1024a(22) =0a(23) =2216a(24) =15a(25) =4096a(26) =258a(27) =8262a(28) =0a(29) =16944