A240466 - OEIS

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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).

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

(list; graph; refs; listen; history; text; internal format)

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

LINKS

Table of n, a(n) for n=1..21.

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

Cf. A000203, A017665, A017666, A028986.

Sequence in context: A073789 A004880 A065666 * A141769 A004891 A037442

Adjacent sequences: A240463 A240464 A240465 * A240467 A240468 A240469

KEYWORD

nonn,base,more

AUTHOR

Michel Marcus, Apr 06 2014

EXTENSIONS

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

STATUS

approved