A141643 Numbers k such that sigma(k)/k = 5/2.

24, 91963648, 10200236032

Offset: 1

Author

Yasutoshi Kohmoto, May 10 2008

Keywords

• nonn
• more
• bref

Comments

There are no other terms through 2^34. - Walter Nissen, Apr 17 2009

No more terms below 10^12. - Jud McCranie, Aug 30 2013

a(4) > 10^100 if it exists. - Max Alekseyev, Jun 05 2025

Links

• G. P. Michon, Multiperfect and hemiperfect numbers
• Walter Nissen, Abundancy : Some Resources
• Walter Nissen, Abundancy : Some Resources
• Walter Nissen, Primitive Friendly Pairs with friends < 2^34 with denom < 20000

Crossrefs

Cf. A055153, A141645, A159271, A160678.

Programs

Mathematica

Select[Range[100000], DivisorSigma[1, #]/# == 5/2 &] (* Robert Price, Apr 03 2019 *)

PARI

isok(k) = sigma(k, -1) == 5/2; \\ Michel Marcus, Apr 04 2019

Extensions

Definition rewritten by M. F. Hasler, May 10 2008

First three terms confirmed by Ray Chandler, Sep 18 2008