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A328265 Integers m such that m and sigma(m) are relatively prime and sigma(sigma(m))/m is an integer. 0
1, 2, 4, 8, 16, 21, 64, 512, 4096, 29127, 65536, 262144, 1073741824, 355744082763 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,2
COMMENTS
1152921504606846976, 309485009821345068724781056, 81129638414606681695789005144064, 85070591730234615865843651857942052864 are also terms.
LINKS
PROG
(PARI) isok(m) = my(s=sigma(m)); (gcd(s, m) == 1) && (denominator(sigma(s)/m) == 1);
CROSSREFS
Cf. A000203 (sigma).
Intersection of A014567 and A019278.
Sequence in context: A196871 A334423 A001856 * A002081 A102039 A045844
KEYWORD
nonn,hard,more
AUTHOR
Michel Marcus, Oct 10 2019
STATUS
approved

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Last modified March 2 08:59 EST 2024. Contains 370461 sequences. (Running on oeis4.)