login
This site is supported by donations to The OEIS Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A055721 Numbers n such that sigma_2(n)/n > sigma_2(k)/k for all k < n. 1
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

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

LINKS

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

MAPLE

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

MATHEMATICA

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

CROSSREFS

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).

Sequence in context: A084925 A045718 A068005 * A064376 A283808 A068578

Adjacent sequences:  A055718 A055719 A055720 * A055722 A055723 A055724

KEYWORD

nonn

AUTHOR

Robert G. Wilson v, Jun 09 2000

EXTENSIONS

Name edited by Michel Marcus, Nov 12 2016

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified September 17 04:03 EDT 2019. Contains 327119 sequences. (Running on oeis4.)