Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #13 Jul 10 2015 23:01:31
%S 1,2,3,4,6,8,9,10,12,15,16,18,20,24,30,36,40,42,48,60,72,80,84,90,96,
%T 120,126,144,168,180,210,240,252,280,288,300,360,420,432,480,504,540,
%U 560,600,630,720,840,900,1008,1080,1260
%N Sigma-crowded numbers: n such that d(n)/sigma(n) is larger than d(m)/sigma(m) for all m > n.
%C Since d(m) < 2*sqrt(m) < 2*sigma(m), we need only test values of m < (2*sigma(n)/d(n))^2.
%H Donovan Johnson, <a href="/A067023/b067023.txt">Table of n, a(n) for n = 1..300</a>
%t crowded[n_] := Module[{}, stop=(2/(dovern=DivisorSigma[0, n]/DivisorSigma[1, n]))^2; For[m=n+1, m<stop, m++, If[DivisorSigma[0, m]/DivisorSigma[1, m] >=dovern, Return[False]]]; True]; Select[Range[1, 13000], crowded]
%Y An analog of A066523. Cf. A002182, A000005, A000203, A004394, A034884, A056758.
%K nonn
%O 1,2
%A _Labos Elemer_, Jan 09 2002