A344102 Numbers k with at least two divisors d for which sigma(k) = d*sigma(d).

16380, 290160, 475020, 1372140, 4754880, 5284356, 5624892, 7033572, 8414640, 10322676, 12203100, 12724908, 16435692, 16655184, 24306480, 35675640, 36203076, 39792060, 43266132, 49758720, 55040076, 68229252, 70142436, 74662476, 76527360, 77084280, 82833660

Offset

1,1

Links

Table of n, a(n) for n=1..27.

Example

sigma(16380) = 156*sigma(156) = 182*sigma(182).
sigma(16655184) = 4368*sigma(4368) = 4836*sigma(4836) = 5642*sigma(5642).

Mathematica

Select[Range[1.5*10^6], Count[(d = Divisors[#]) * DivisorSigma[1, d], DivisorSigma[1, #]] > 1 &] (* Amiram Eldar, May 12 2021 *)

Prog

(Magma) s:=func<n|{d:d in Divisors(n)|DivisorSigma(1, n) eq DivisorSigma(1, d)*d}>;  [n: n in [1..1000000]|#s(n) ge 2];

Crossrefs

Cf. A000203, A339472, A344103.

Sequence in context: A223109 A126824 A236778 * A307493 A075958 A075963

Adjacent sequences: A344099 A344100 A344101 * A344103 A344104 A344105

Keyword

nonn

Author

Marius A. Burtea, May 10 2021

Status

approved