a(n) = 6*2^n + 4 (Bode Number A003461(n+2)) except for a(1)=6.

Terms

a(0) =6a(1) =28a(2) =52a(3) =100a(4) =196a(5) =388a(6) =772a(7) =1540a(8) =3076a(9) =6148a(10) =12292a(11) =24580a(12) =49156a(13) =98308a(14) =196612a(15) =393220a(16) =786436a(17) =1572868a(18) =3145732a(19) =6291460a(20) =12582916a(21) =25165828a(22) =50331652a(23) =100663300a(24) =201326596a(25) =402653188a(26) =805306372a(27) =1610612740a(28) =3221225476a(29) =6442450948