A328265 Integers m such that m and sigma(m) are relatively prime and sigma(sigma(m))/m is an integer.

1, 2, 4, 8, 16, 21, 64, 512, 4096, 29127, 65536, 262144, 1073741824, 355744082763

Offset

1,2

Comments

1152921504606846976, 309485009821345068724781056, 81129638414606681695789005144064, 85070591730234615865843651857942052864 are also terms.

Links

Table of n, a(n) for n=1..14.

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: A334423 A375006 A001856 * A002081 A102039 A045844

Adjacent sequences: A328262 A328263 A328264 * A328266 A328267 A328268

Keyword

nonn,hard,more

Author

Michel Marcus, Oct 10 2019

Status

approved