This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A046261 #11 Oct 10 2019 00:37:17
%S A046261 1,3,9,7,8,4,9,8,656,9,9,1771,1441,323,969,434,7,9,9,162261,44,353,
%T A046261 313,414,282,88,828,484,767,3773,94649,767,888,5665,6996,999,999,909,
%U A046261 2992,76267,545,717,989,707,232,55,959,8778,6336,32923,7897987,3693963,989
%N A046261 Largest palindromic substring in 3^n.
%H A046261 Harvey P. Dale, <a href="/A046261/b046261.txt">Table of n, a(n) for n = 0..500</a>
%t A046261 Max/@Table[Select[FromDigits/@Flatten[Table[Partition[ IntegerDigits[ 3^k], n,1],{n,IntegerLength[3^k]}],1],PalindromeQ],{k,0,60}] (* Requires Mathematica version 10 or later *) (* _Harvey P. Dale_, Sep 25 2018 *)
%Y A046261 Cf. A046269.
%K A046261 nonn,base
%O A046261 0,2
%A A046261 _Patrick De Geest_, Jun 15 1998