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

Terms

a(0) =1a(1) =5a(2) =15a(3) =37a(4) =83a(5) =177a(6) =367a(7) =749a(8) =1515a(9) =3049a(10) =6119a(11) =12261a(12) =24547a(13) =49121a(14) =98271a(15) =196573a(16) =393179a(17) =786393a(18) =1572823a(19) =3145685a(20) =6291411a(21) =12582865a(22) =25165775a(23) =50331597a(24) =100663243a(25) =201326537a(26) =402653127a(27) =805306309a(28) =1610612675a(29) =3221225409