login
This site is supported by donations to The OEIS Foundation.

 

Logo

Thanks to everyone who made a donation during our annual appeal!
To see the list of donors, or make a donation, see the OEIS Foundation home page.

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A074873 Friendly numbers (see A074902) such that sigma(n) is not friendly. 0
66, 210, 282, 364, 510, 642, 930, 966, 1080, 1092, 1146, 1624, 2130, 2226, 2346, 2586, 2676, 3560, 3810, 4278, 4872, 7965 (list; graph; refs; listen; history; text; internal format)
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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified January 20 02:05 EST 2019. Contains 319320 sequences. (Running on oeis4.)