Largest prime <= 7^n.

Terms

a(0) =7a(1) =47a(2) =337a(3) =2399a(4) =16787a(5) =117643a(6) =823541a(7) =5764799a(8) =40353601a(9) =282475241a(10) =1977326699a(11) =13841287199a(12) =96889010371a(13) =678223072817