2^n - number of digits of 2^n.

Terms

a(0) =0a(1) =1a(2) =3a(3) =7a(4) =14a(5) =30a(6) =62a(7) =125a(8) =253a(9) =509a(10) =1020a(11) =2044a(12) =4092a(13) =8188a(14) =16379a(15) =32763a(16) =65531a(17) =131066a(18) =262138a(19) =524282a(20) =1048569a(21) =2097145a(22) =4194297a(23) =8388601a(24) =16777208a(25) =33554424a(26) =67108856a(27) =134217719a(28) =268435447a(29) =536870903