a(n) is the sum of (2^n mod k) for odd numbers k < 2^(n-1).

Terms

a(0) =0a(1) =0a(2) =2a(3) =4a(4) =31a(5) =103a(6) =439a(7) =1665a(8) =6942a(9) =27598a(10) =110371a(11) =438843a(12) =1762848a(13) =7052170a(14) =28211223a(15) =112799719a(16) =451277874a(17) =1804973952a(18) =7220128542a(19) =28880086112a(20) =115521335176a(21) =462085087138