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 A259918 #4 Jul 14 2015 16:39:17 %S A259918 6,30,80,40,12,84,66,78,102,114,240,138,120,150,174,135,186,864,222, %T A259918 246,60,258,282,560,318,330,354,366,720,390,402,426,360,438,880,474, %U A259918 498,510,440,534,132,1040,570,582,606,618,520,924,642,654,678,690,540,726 %N A259918 Friendly numbers that are smallest in their clubs, ordered by the second-smallest member of the clubs. %C A259918 Subsequence of A259917 (see that entry). %H A259918 Wikipedia, <a href="https://en.wikipedia.org/wiki/Friendly_number">Friendly number</a>. %o A259918 (PARI) known=List();for(i=1,10^5,a=sigma(i)/i;match=0;for(j=1,#known,if(known[j][1]==a,match=j;break()));if(match,old=known[match][2];if(old,print1(old,", ");known[match]=[a,0]),listput(known,[a,i]))) %Y A259918 Cf. A259917, A050973, A095301, A014567. %K A259918 nonn %O A259918 1,1 %A A259918 _Jeppe Stig Nielsen_, Jul 08 2015