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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).
0
1, 2, 3, 4, 5, 6, 7, 333, 17571, 40004, 93939, 569965, 1787871, 2316132, 541626145, 17575757571, 5806270726085, 7359770779537, 520524424425025, 17275787578757271, 17878787578787871
OFFSET
1,2
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
PROG
(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)));
CROSSREFS
KEYWORD
nonn,base,more
AUTHOR
Michel Marcus, Apr 06 2014
EXTENSIONS
a(16)-a(21) from Hiroaki Yamanouchi, Sep 27 2014
STATUS
approved