a(n) = 2^n - 9.

Terms

a(0) =-8a(1) =-7a(2) =-5a(3) =-1a(4) =7a(5) =23a(6) =55a(7) =119a(8) =247a(9) =503a(10) =1015a(11) =2039a(12) =4087a(13) =8183a(14) =16375a(15) =32759a(16) =65527a(17) =131063a(18) =262135a(19) =524279a(20) =1048567a(21) =2097143a(22) =4194295a(23) =8388599a(24) =16777207a(25) =33554423a(26) =67108855a(27) =134217719a(28) =268435447a(29) =536870903