a(n) = 2^n - (2^(n-1) mod n), where "mod" is the nonnegative remainder operator.

Terms

a(0) =2a(1) =4a(2) =7a(3) =16a(4) =31a(5) =62a(6) =127a(7) =256a(8) =508a(9) =1022a(10) =2047a(11) =4088a(12) =8191a(13) =16382a(14) =32764a(15) =65536a(16) =131071a(17) =262130a(18) =524287a(19) =1048568a(20) =2097148a(21) =4194302a(22) =8388607a(23) =16777208a(24) =33554416a(25) =67108862a(26) =134217715a(27) =268435448a(28) =536870911a(29) =1073741822