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A327630 a(n) is the least integer k such that sigma(sigma(k)) >= n*k where sigma is A000203, the sum of divisors. 1
1, 2, 6, 6, 24, 24, 24, 60, 120, 480, 540, 1560, 2520, 10920, 27720, 30240, 191520, 360360, 360360, 3243240, 5765760, 28828800, 109549440, 438197760, 766846080, 3834230400, 9081072000, 32974381440, 147516969600, 880887047040, 2802822422400 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

From Daniel Suteu, Oct 10 2019: (Start)

a(32) <= 14814918518400,

a(33) <= 64464915715200,

a(34) <= 709114072867200,

a(35) <= 9881550651772800,

a(36) <= 76648784785372800,

a(37) <= 2376112328346556800. (End)

LINKS

Table of n, a(n) for n=1..31.

PROG

(PARI) a(n) = my(k=1); while (sigma(sigma(k))/k < n, k++); k;

CROSSREFS

Cf. A000203, A007539, A023199, A098221, A019278.

Cf. A051027, A272930.

Sequence in context: A304680 A325803 A130865 * A282170 A105725 A005226

Adjacent sequences:  A327627 A327628 A327629 * A327631 A327632 A327633

KEYWORD

nonn,more

AUTHOR

Michel Marcus, Oct 07 2019

EXTENSIONS

a(23)-a(29) from Giovanni Resta, Oct 07 2019

a(30)-a(31) from Giovanni Resta, Feb 27 2020

STATUS

approved

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Last modified May 13 23:41 EDT 2021. Contains 343868 sequences. (Running on oeis4.)