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 A240466 #21 Sep 29 2014 12:21:12 %S A240466 1,2,3,4,5,6,7,333,17571,40004,93939,569965,1787871,2316132,541626145, %T A240466 17575757571,5806270726085,7359770779537,520524424425025, %U A240466 17275787578757271,17878787578787871 %N A240466 Palindromes for which both the numerator (A017665) and the denominator (A017666) of sigma(n)/n are palindromes, where sigma is the sum of divisors (A000203). %C A240466 Compare with A028986 (Palindromes whose sum of divisors is palindromic). %C A240466 These terms of A028986 also belong here: 1, 2, 3, 4, 5, 7, 333, 17571, 1787871, 541626145, 17575757571, 5806270726085, 7359770779537. %C A240466 a(22) > 10^18. - _Hiroaki Yamanouchi_, Sep 27 2014 %o A240466 (PARI) reverse(expr)=my(v=Vec(Str(expr)),n=length(v));eval(concat(vector(n,i,v[n-i+1]))); %o A240466 isok(n) = (rn = reverse(n)) && (rn == n) && (ab = sigma(n)/n) && (abr = sigma(rn)/rn) && (numerator(abr) == reverse(numerator(ab))) && (denominator(abr) == reverse(denominator(ab))); %Y A240466 Cf. A000203, A017665, A017666, A028986. %K A240466 nonn,base,more %O A240466 1,2 %A A240466 _Michel Marcus_, Apr 06 2014 %E A240466 a(16)-a(21) from _Hiroaki Yamanouchi_, Sep 27 2014