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 A240453 #23 Dec 06 2021 16:21:14
%S A240453 11,11,11,11,11,11,11,11,11,13,101,37,11,131,47,151,23,19,181,13,11,
%T A240453 101,53,37,29,11,11,131,17,13,283,293,101,313,19,37,11,353,11,13,17,
%U A240453 11,197,101,23,53,31,37,227,13,31,19,97,11,101,103,11,107,109,13
%N A240453 Greatest prime divisors of the palindromes with an even number of digits.
%C A240453 Greatest prime divisor of A056524(n), or greatest prime divisor of the concatenation of a number n and reverse(n).
%C A240453 The palindromes with an even number of digits are composite numbers divisible by 11. There are many palindromic prime divisors, such as 11, 101, 131, 151, 181, 313, 353, ..., 30103, ...
%H A240453 Michel Lagneau, <a href="/A240453/b240453.txt">Table of n, a(n) for n = 1..10000</a>
%F A240453 a(n) = A006530(A056524(n)).
%e A240453 a(10) = 13 because the concatenation of 10 and 01 is 1001 = 7*11*13 where 13 is the greatest divisor of 1001.
%p A240453 with(numtheory):for n from 1 to 100 do:x:=convert(n,base,10):n1:=nops(x): s:=sum('x[i]*10^(n1-i)', 'i'=1..n1):y:=n*10^n1+s:z:=factorset(y):n2:=nops(z):d:=z[n2]:printf(`%d, `,d):od:
%t A240453 d[n_]:=IntegerDigits[n];Table[FactorInteger[FromDigits[Join[x=d[n],Reverse[x]]]][[-1,1]],{n,1,100}]
%t A240453 FactorInteger[#][[-1,1]]&/@Flatten[Table[Select[Range[10^n,10^(n+1)-1],PalindromeQ],{n,1,3,2}]] (* _Harvey P. Dale_, Dec 06 2021 *)
%o A240453 (Python)
%o A240453 from sympy import primefactors
%o A240453 def a(n): s = str(n); return max(primefactors(int(s + s[::-1])))
%o A240453 print([a(n) for n in range(1, 61)]) # _Michael S. Branicky_, Nov 11 2021
%Y A240453 Cf. A056524, A006530, A066492, A240454.
%K A240453 nonn,base,easy
%O A240453 1,1
%A A240453 _Michel Lagneau_, Apr 05 2014