a(n) = 16*2^n - 11 (n>=1).

Terms

a(0) =21a(1) =53a(2) =117a(3) =245a(4) =501a(5) =1013a(6) =2037a(7) =4085a(8) =8181a(9) =16373a(10) =32757a(11) =65525a(12) =131061a(13) =262133a(14) =524277a(15) =1048565a(16) =2097141a(17) =4194293a(18) =8388597a(19) =16777205a(20) =33554421a(21) =67108853a(22) =134217717a(23) =268435445a(24) =536870901a(25) =1073741813a(26) =2147483637a(27) =4294967285a(28) =8589934581a(29) =17179869173