a(n) = Sum_{k<n} ((2^n-1) mod (2^k-1)).

Terms

a(0) =0a(1) =0a(2) =1a(3) =1a(4) =5a(5) =4a(6) =13a(7) =14a(8) =28a(9) =30a(10) =69a(11) =60a(12) =131a(13) =144a(14) =263a(15) =267a(16) =549a(17) =530a(18) =1077a(19) =1100a(20) =2085a(21) =2140a(22) =4301a(23) =4186a(24) =8364a(25) =8558a(26) =16623a(27) =16744a(28) =33515a(29) =33164