a(0) = 8; for n>0, a(n) = 2*a(n-1) - 1.

Terms

a(0) =8a(1) =15a(2) =29a(3) =57a(4) =113a(5) =225a(6) =449a(7) =897a(8) =1793a(9) =3585a(10) =7169a(11) =14337a(12) =28673a(13) =57345a(14) =114689a(15) =229377a(16) =458753a(17) =917505a(18) =1835009a(19) =3670017a(20) =7340033a(21) =14680065a(22) =29360129a(23) =58720257a(24) =117440513a(25) =234881025a(26) =469762049a(27) =939524097a(28) =1879048193a(29) =3758096385