Largest palindromic substring in 6^n.

Terms

a(0) =1a(1) =6a(2) =6a(3) =6a(4) =9a(5) =777a(6) =656a(7) =99a(8) =616a(9) =696a(10) =66a(11) =797a(12) =767a(13) =606a(14) =9a(15) =9a(16) =282a(17) =444a(18) =5995a(19) =9a(20) =656a(21) =77a(22) =131a(23) =22a(24) =838a(25) =2992a(26) =9a(27) =77a(28) =464a(29) =89298