a(n) = 2^n + n + 1.

Terms

a(0) =2a(1) =4a(2) =7a(3) =12a(4) =21a(5) =38a(6) =71a(7) =136a(8) =265a(9) =522a(10) =1035a(11) =2060a(12) =4109a(13) =8206a(14) =16399a(15) =32784a(16) =65553a(17) =131090a(18) =262163a(19) =524308a(20) =1048597a(21) =2097174a(22) =4194327a(23) =8388632a(24) =16777241a(25) =33554458a(26) =67108891a(27) =134217756a(28) =268435485a(29) =536870942