Largest prime substring in 3^n (0 if none).

Terms

a(0) =0a(1) =3a(2) =0a(3) =7a(4) =0a(5) =43a(6) =29a(7) =7a(8) =61a(9) =683a(10) =9049a(11) =71a(12) =53a(13) =59a(14) =7829a(15) =4348907a(16) =3046721a(17) =40163a(18) =89a(19) =62261467a(20) =84401a(21) =353203a(22) =1381a(23) =941a(24) =2429536481a(25) =288609443a(26) =8329a(27) =6255974849a(28) =876792454961a(29) =77364883