A347247 Numbers k such that the greatest prime factor of A000593(k) [the sum of their odd divisors] is at least as large as the greatest prime factor of k itself.

1, 9, 18, 25, 27, 36, 45, 49, 50, 54, 63, 72, 75, 81, 90, 98, 99, 100, 108, 117, 121, 125, 126, 135, 144, 147, 150, 162, 169, 175, 180, 196, 198, 200, 216, 225, 234, 242, 243, 245, 250, 252, 270, 275, 288, 289, 294, 300, 315, 324, 325, 338, 350, 360, 361, 363, 375, 392, 396, 400, 405, 425, 432, 441, 450, 468, 475

Offset

1,2

Comments

The initial 1 is included on the grounds that A006530(1) = 1 and A000593(1) = 1. After 1, if k is included as a term, then also 2*k is present.

A038838(27) = 153 is the first term of A038838 not present here.

Links

Paolo Xausa, Table of n, a(n) for n = 1..10000

Mathematica

A347247Q[k_] := FactorInteger[DivisorSum[k, # &, OddQ]][[-1, 1]] >= FactorInteger[k][[-1, 1]];
Select[Range[500], A347247Q] (* Paolo Xausa, Jan 01 2026 *)

Crossrefs

Cf. A000593, A006530, A347246 (characteristic function), A347248 (complement).

Apart from the initial 1, a subsequence of A347242.

Cf. also A038838.

Sequence in context: A390365 A347242 A038838 * A038837 A325359 A307579

Adjacent sequences: A347244 A347245 A347246 * A347248 A347249 A347250

Keyword

nonn

Author

Antti Karttunen, Aug 28 2021

Status

approved