login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A077567 Least k >= 2 such that sigma(n) divides sigma(n^k). 1
2, 3, 3, 4, 3, 3, 3, 5, 4, 3, 3, 5, 3, 3, 3, 6, 3, 7, 3, 5, 3, 3, 3, 3, 4, 3, 5, 7, 3, 3, 3, 7, 3, 3, 3, 4, 3, 3, 3, 5, 3, 3, 3, 5, 3, 3, 3, 11, 4, 7, 3, 7, 3, 5, 3, 3, 3, 3, 3, 5, 3, 3, 7, 8, 3, 3, 3, 5, 3, 3, 3, 13, 3, 3, 7, 5, 3, 3, 3, 5, 6, 3, 3, 5, 3, 3, 3, 5, 3, 3, 3, 5, 3, 3, 3, 7, 3, 4, 7, 4, 3, 3, 3 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

From Robert Israel, Mar 14 2017: (Start)

If x and y are coprime and a(x)=a(y)=k, then a(xy)=k as well.

If n > 1 is squarefree, then a(n^k) = k+2 for all k>=1.

Is there any n > 1 with a(n) = 2? (End)

LINKS

Robert Israel, Table of n, a(n) for n = 1..10000

MAPLE

f:= proc(n) local k, s; uses numtheory;

  s:= sigma(n);

  for k from 2 do if sigma(n^k) mod s = 0 then return k fi

  od

end proc:

map(f, [$1..200]); # Robert Israel, Mar 14 2017

MATHEMATICA

a[n_] := For[k = 2, True, k++, If[Divisible[DivisorSigma[1, n^k], DivisorSigma[1, n]], Return[k]]];

Array[a, 100] (* Jean-Fran├žois Alcover, Aug 24 2020 *)

CROSSREFS

Sequence in context: A139069 A071866 A077603 * A096344 A030349 A285203

Adjacent sequences:  A077564 A077565 A077566 * A077568 A077569 A077570

KEYWORD

nonn

AUTHOR

Benoit Cloitre, Dec 01 2002

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 18 03:35 EDT 2020. Contains 337164 sequences. (Running on oeis4.)