A327630 a(n) is the least integer k such that sigma(sigma(k)) >= n*k where sigma is A000203, the sum of divisors.

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

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: A367765 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