Largest palindromic substring in 4^n.

Terms

a(0) =1a(1) =4a(2) =6a(3) =6a(4) =6a(5) =4a(6) =9a(7) =8a(8) =55a(9) =262a(10) =8a(11) =9a(12) =777a(13) =88a(14) =545a(15) =737a(16) =949a(17) =717a(18) =767a(19) =77a(20) =777a(21) =111a(22) =444a(23) =77a(24) =767a(25) =42624a(26) =737a(27) =9a(28) =575a(29) =7117