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).

1, 2, 3, 4, 5, 6, 7, 333, 17571, 40004, 93939, 569965, 1787871, 2316132, 541626145, 17575757571, 5806270726085, 7359770779537, 520524424425025, 17275787578757271, 17878787578787871

Offset: 1

Author

Michel Marcus, Apr 06 2014

Keywords

• nonn
• base
• more

Comments

Compare with A028986 (Palindromes whose sum of divisors is palindromic).

These terms of A028986 also belong here: 1, 2, 3, 4, 5, 7, 333, 17571, 1787871, 541626145, 17575757571, 5806270726085, 7359770779537.

a(22) > 10^18. - Hiroaki Yamanouchi, Sep 27 2014

Crossrefs

Cf. A000203, A017665, A017666, A028986.

Programs

PARI

reverse(expr)=my(v=Vec(Str(expr)),n=length(v));eval(concat(vector(n,i,v[n-i+1])));
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)));

Extensions

a(16)-a(21) from Hiroaki Yamanouchi, Sep 27 2014