a(n) = 4*7^n+1.

Terms

a(0) =5a(1) =29a(2) =197a(3) =1373a(4) =9605a(5) =67229a(6) =470597a(7) =3294173a(8) =23059205a(9) =161414429a(10) =1129900997a(11) =7909306973a(12) =55365148805a(13) =387556041629