Largest prime substring in 9^n (0 if none).

Terms

a(0) =0a(1) =0a(2) =0a(3) =29a(4) =61a(5) =9049a(6) =53a(7) =7829a(8) =3046721a(9) =89a(10) =84401a(11) =1381a(12) =2429536481a(13) =8329a(14) =876792454961a(15) =113209a(16) =853020188851a(18) =15009463529a(19) =35085171767a(22) =984770902183