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A327599 Odd numbers k that have a divisor d such that sigma(d)*d is equal to k. 3
1, 117, 775, 2793, 9801, 16093, 30927, 88723, 90675, 137541, 292537, 326781, 488125, 732511, 796797, 954273, 1882881, 1926183, 2164575, 2896363, 3500157, 3618459, 4985713, 6725201, 7595775, 8042167, 10380591, 12326221, 12472075, 14076543, 16092297, 20456373, 23968425, 25774633 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

We need d and sigma(d) odd which happens precisely when d is an odd square.

LINKS

David A. Corneth, Table of n, a(n) for n = 1..10000

EXAMPLE

As 9 * sigma(9) = 9 * (1 + 3 + 9) = 9 * 13 = 117 is odd, 117 is in the sequence.

MATHEMATICA

Select[2Range[0, 9999] + 1, MemberQ[(DivisorSigma[1, #] * # &)/@Divisors[#], #] &] (* Alonso del Arte, Sep 18 2019 *)

PROG

(PARI) upto(n) = {my(res = List()); forstep(i = 1, sqrtnint(n, 4), 2, c = i^2*sigma(i^2); if(c <= n, listput(res, c))); listsort(res, 1); res}

CROSSREFS

Odd terms of A327165.

Cf. A064987.

Sequence in context: A217798 A252853 A273125 * A326064 A233376 A233051

Adjacent sequences: A327596 A327597 A327598 * A327600 A327601 A327602

KEYWORD

nonn

AUTHOR

David A. Corneth, Sep 18 2019

STATUS

approved

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Last modified February 3 04:25 EST 2023. Contains 360024 sequences. (Running on oeis4.)