A068400 Numbers k such that sigma(k) = phi(k*bigomega(k)).

248, 357, 1045, 3596, 3956, 4064, 5396, 8636, 20026, 20320, 23374, 24871, 25714, 29029, 33915, 35074, 39585, 41656, 50065, 55154, 56134, 56536, 58435, 61344, 64285, 74613, 79000, 87087, 87685, 137885, 140335, 142240, 353133, 383656, 393104, 423657, 474548, 479864

Offset: 1

Author

Benoit Cloitre, Mar 02 2002

Keywords

• nonn

Comments

For all the numbers listed, gcd(n!-1,2^n+1) = 2n+1. Is this always true? - Giovanni Resta, Nov 15 2006

This is plausible and true for n up to 45000. - Max Alekseyev, Nov 16 2006

Examples

			248 = 31*2^3 is here because sigma(248) = 480 = eulerphi(248*bigomega(2^3 * 31)) = eulerphi(248*4). - _David A. Corneth_, Jun 29 2025
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A000010 (phi), A000203 (sigma), A001222 (bigomega), A074891.

Programs

PARI

isok(k) = {my(f = factor(k)); sigma(f) == eulerphi(k * bigomega(f));} \\ Amiram Eldar, May 09 2025