cp's OEIS Frontend

A055721 Numbers n such that sigma_2(n)/n > sigma_2(k)/k for all k < n.

%I A055721 #23 Aug 04 2019 06:38:19
%S A055721 1,2,3,4,6,8,10,12,14,16,18,20,22,24,28,30,36,40,42,48,54,60,66,70,72,
%T A055721 78,80,84,90,96,108,120,132,140,144,150,156,168,180,192,204,210,216,
%U A055721 228,240,252,264,270,276,288,300,312,324,330,336,348,360,384,396,408
%N A055721 Numbers n such that sigma_2(n)/n > sigma_2(k)/k for all k < n.
%C A055721 sigma_2(n) is the sum of the squares of the divisors of n (A001157).
%H A055721 Amiram Eldar, <a href="/A055721/b055721.txt">Table of n, a(n) for n = 1..6000</a> (terms 1..1000 from Ivan Neretin)
%p A055721 m:= 0: res:= NULL:
%p A055721 for n from 1 to 500 do
%p A055721   r:= numtheory:-sigma[2](n)/n;
%p A055721   if r > m then
%p A055721     m:= r;
%p A055721     res:= res, n;
%p A055721   fi
%p A055721 od:
%p A055721 res; # _Robert Israel_, Nov 12 2016
%t A055721 a=0; Do[b=DivisorSigma[2, n]/n; If[b>a, a=b; Print[n]], {n, 1, 10^7}]
%Y A055721 Cf. A002182 (records of sigma_0(n)), A002093 (records of sigma_1(n)), A004394 (records of sigma_1(n)/n), A193988 (records of sigma_2(n)), A208767 (records of sigma_2(n)/n^2).
%K A055721 nonn
%O A055721 1,2
%A A055721 _Robert G. Wilson v_, Jun 09 2000
%E A055721 Name edited by _Michel Marcus_, Nov 12 2016