a(n) = 7*2^n - 6.

Terms

a(0) =1a(1) =8a(2) =22a(3) =50a(4) =106a(5) =218a(6) =442a(7) =890a(8) =1786a(9) =3578a(10) =7162a(11) =14330a(12) =28666a(13) =57338a(14) =114682a(15) =229370a(16) =458746a(17) =917498a(18) =1835002a(19) =3670010a(20) =7340026a(21) =14680058a(22) =29360122a(23) =58720250a(24) =117440506a(25) =234881018a(26) =469762042a(27) =939524090a(28) =1879048186a(29) =3758096378