This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A074873 #13 Mar 05 2015 04:01:33 %S A074873 66,210,282,364,510,642,930,966,1080,1092,1146,1624,2130,2226,2346, %T A074873 2586,2676,3560,3810,4278,4872,7965 %N A074873 Friendly numbers (see A074902) such that sigma(n) is not friendly. %C A074873 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 %C A074873 From _Walter Nissen_, May 28 2011: (Start) %C A074873 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. %C A074873 Numbers without friends are called solitary. %C A074873 (End) %e A074873 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. %K A074873 nonn %O A074873 0,1 %A A074873 _Jon Perry_, Sep 12 2002