A327165 Numbers n that have a divisor d such that sigma(d)*d is equal to n.

1, 6, 12, 28, 30, 56, 72, 117, 120, 132, 180, 182, 306, 336, 360, 380, 496, 552, 672, 702, 775, 792, 840, 870, 992, 1080, 1092, 1406, 1440, 1568, 1584, 1680, 1722, 1836, 1892, 2016, 2160, 2184, 2256, 2280, 2793, 2862, 3276, 3312, 3510, 3540, 3600, 3672, 3696, 3782, 3960, 4032, 4556, 4560, 4650, 5096, 5112, 5220

Offset: 1

Author

Antti Karttunen, Sep 18 2019

Keywords

• nonn

Comments

Numbers n for which A327153(n) > 0.

Sequence A064987 sorted into ascending order, with duplicates removed.

All even terms of A000396 occur here.

Links

• Antti Karttunen, Table of n, a(n) for n = 1..10001

Crossrefs

Cf. A000203, A000396, A064987, A327153, A327599 (subsequence of odd terms).

Programs

PARI

isA327165(n) = { fordiv(n, d, if(n==d*sigma(d),return(1))); (0); };

PARI

A327165list(up_to) = { my(res = List()); for(i = 1, sqrtint(up_to), c = i*sigma(i); if(c <= up_to, listput(res, c))); listsort(res, 1); Vec(res); }; \\ From David A. Corneth, Sep 18 2019