A074873 Friendly numbers (see A074902) such that sigma(n) is not friendly.

66, 210, 282, 364, 510, 642, 930, 966, 1080, 1092, 1146, 1624, 2130, 2226, 2346, 2586, 2676, 3560, 3810, 4278, 4872, 7965

Offset

0,1

Comments

I do not know how rigorously these numbers have been established. It is possible there are missing terms - see A074902. - N. J. A. Sloane, Sep 15 2002

From Walter Nissen, May 28 2011: (Start)

Yes; in particular, if perchance 10 should turn out to have a friend, then 10 would be a(0). Also 30 and 40 might possibly be in this sequence.

Numbers without friends are called solitary.

(End)

Links

Table of n, a(n) for n=0..21.

Example

6 is friendly, but so is sigma(6)=12, so 6 is not in the sequence. 210 is friendly (with 17360 for example), but sigma(210)=576 is not friendly.

Crossrefs

Sequence in context: A255102 A202647 A202640 * A205817 A046393 A268582

Adjacent sequences: A074870 A074871 A074872 * A074874 A074875 A074876

Keyword

nonn

Author

Jon Perry, Sep 12 2002

Status

approved