a(0) = 0, a(1) = 1, for n > 1, a(n) = 2^n - (sigma((2^n)-1) - sigma((2^(n-1))-1)).

Terms

a(0) =0a(1) =1a(2) =1a(3) =4a(4) =0a(5) =24a(6) =-8a(7) =104a(8) =-48a(9) =352a(10) =80a(11) =1424a(12) =-2480a(13) =8736a(14) =2048a(15) =16384a(16) =-7008a(17) =111456a(18) =-80384a(19) =473600a(20) =-427008a(21) =1630976a(22) =750592a(23) =5731232a(24) =-12709664a(25) =36894720a(26) =12300416a(27) =68246368a(28) =-38345568a(29) =459223232