A208767 -id:A208767 - cp's OEIS frontend

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

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, 78, 80, 84, 90, 96, 108, 120, 132, 140, 144, 150, 156, 168, 180, 192, 204, 210, 216, 228, 240, 252, 264, 270, 276, 288, 300, 312, 324, 330, 336, 348, 360, 384, 396, 408

Offset: 1

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Robert G. Wilson v, Jun 09 2000

nonn

sigma_2(n) is the sum of the squares of the divisors of n (A001157).

Amiram Eldar, Table of n, a(n) for n = 1..6000 (terms 1..1000 from Ivan Neretin)

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).

m:= 0: res:= NULL:
for n from 1 to 500 do
  r:= numtheory:-sigma[2](n)/n;
  if r > m then
    m:= r;
    res:= res, n;
  fi
od:
res; # Robert Israel, Nov 12 2016

a=0; Do[b=DivisorSigma[2, n]/n; If[b>a, a=b; Print[n]], {n, 1, 10^7}]

Name edited by Michel Marcus, Nov 12 2016

cp's OEIS Frontend

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

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