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 A050973 #32 Feb 16 2025 08:32:41
%S A050973 28,140,200,224,234,270,308,364,476,496,496,532,600,644,672,700,812,
%T A050973 819,868,936,1036,1148,1170,1204,1316,1400,1484,1488,1488,1540,1638,
%U A050973 1638,1638,1652,1708,1800,1820,1876,1988,2016,2044,2200,2212,2324
%N A050973 Larger member of friendly pairs ordered by smallest maximal element.
%C A050973 Perfect numbers greater than 6 (A000396) belong to this sequence as they form friendly pairs with smaller perfect, so that the n-th perfect number will appear n-1 times in the sequence. - _Michel Marcus_, Dec 03 2013
%C A050973 If we remove duplicates from the sequence we get A095301. - _Jeppe Stig Nielsen_, Jul 08 2015
%C A050973 It is possible to derive a friendly pair from 2 existing pairs (a_n,b_n) and (a_k,b_k); if (a_n,b_k) and (a_k,b_n) (resp. (a_k,b_k) and (a_n,b_n)) are coprime, then (a_n*b_k,a_k*b_n) (resp. (a_k*b_k,a_n*b_n)) is a friendly pair. For instance one can derive (32760,30240) from (819,135) and (224,40). Moreover, since 32760/35 and 30240/35 are both coprime to 35, one can also derive the primitive friendly pair (936,864). - _Michel Marcus_, Oct 09 2015
%H A050973 Donovan Johnson, <a href="/A050973/b050973.txt">Table of n, a(n) for n = 1..10000</a>
%H A050973 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/FriendlyPair.html">Friendly Pair</a>.
%o A050973 (PARI) lista(nn) = {for (n=1, nn, ab = sigma(n)/n; for (i=2, n-1, if (sigma(i)/i == ab, print1(n, ", "));););} \\ _Michel Marcus_, Dec 03 2013
%Y A050973 Cf. A050972, A074902, A095301.
%K A050973 nonn
%O A050973 1,1
%A A050973 _Eric W. Weisstein_