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 A339680 #4 Dec 12 2020 19:52:34
%S A339680 220,280540,1669910,56512610,133089500,8376676490,24631297425,
%T A339680 688539661425,724641414350,92371445691525,3599848247084570,
%U A339680 7526776592305828,14223210473604152536,35367855263480783043
%N A339680 Lesser of amicable pair a < b such that the ratio of their number of divisors d(a)/d(b) sets a new record.
%C A339680 The larger counterparts are in A339681.
%C A339680 The corresponding ratios are 2, 3, 4, 16/3, 8, 12, 16, 18, 24, 27, 32, 48, 64, 96, ...
%C A339680 The terms were calculated using data from Chernykh's site.
%H A339680 Sergei Chernykh, <a href="http://sech.me/ap/">Amicable pairs list</a>.
%e A339680 The least pair of amicable numbers, (220, 284), has a ratio of the numbers of divisors d(220)/d(284) = 12/6 = 2.
%e A339680 The next pair with a larger ratio is (280540, 365084) whose ratio is d(280540)/d(365084) = 36/12 = 3.
%t A339680 s[n_] := DivisorSigma[1, n] - n; rm = 0; seq = {}; Do[m = s[n]; If[m > n && s[m] == n && (r = Divide @@ DivisorSigma[0, {n, m}]) > rm, rm = r; AppendTo[seq, n]], {n, 1, 10^7}]; seq
%Y A339680 Cf. A000005, A002025, A002046, A063990, A328063, A339681.
%K A339680 nonn,more
%O A339680 1,1
%A A339680 _Amiram Eldar_, Dec 12 2020