A090777 Numbers k such that sigma(k) divides k^2.

1, 6, 28, 120, 364, 496, 672, 840, 1080, 1488, 1782, 2280, 3276, 3472, 7440, 8128, 8736, 11880, 12400, 18360, 20832, 24384, 25296, 26208, 30240, 30256, 32760, 35640, 37200, 56896, 57240, 84360, 86800, 90768, 115560, 121920, 131040, 149856, 170688

Offset

1,2

Links

Donovan Johnson, Table of n, a(n) for n = 1..1000

Mathematica

Select[Range[200000], Divisible[#^2, DivisorSigma[1, #]] &] (* Amiram Eldar, May 09 2022 *)

Prog

(PARI) for (n=1, 10^6, if ( n^2 % sigma(n) ==0, print1(n, ", "))); /* Joerg Arndt, May 28 2012 */

Crossrefs

Cf. A000203, A000290.

Sequence in context: A183013 A325639 A055717 * A055715 A026031 A002694

Adjacent sequences: A090774 A090775 A090776 * A090778 A090779 A090780

Keyword

nonn

Author

Benoit Cloitre, Feb 08 2004

Status

approved