a(n) = 6*2^n - 5.

Terms

a(0) =1a(1) =7a(2) =19a(3) =43a(4) =91a(5) =187a(6) =379a(7) =763a(8) =1531a(9) =3067a(10) =6139a(11) =12283a(12) =24571a(13) =49147a(14) =98299a(15) =196603a(16) =393211a(17) =786427a(18) =1572859a(19) =3145723a(20) =6291451a(21) =12582907a(22) =25165819a(23) =50331643a(24) =100663291a(25) =201326587a(26) =402653179a(27) =805306363a(28) =1610612731a(29) =3221225467