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A123623 Smallest k>1 such that mu(n*k) = mu(n), where mu=A008683. 3
6, 15, 10, 2, 6, 35, 6, 2, 2, 21, 6, 2, 6, 15, 14, 2, 6, 2, 6, 2, 10, 15, 6, 2, 2, 15, 2, 2, 6, 77, 6, 2, 10, 15, 6, 2, 6, 15, 10, 2, 6, 55, 6, 2, 2, 15, 6, 2, 2, 2, 10, 2, 6, 2, 6, 2, 10, 15, 6, 2, 6, 15, 2, 2, 6, 35, 6, 2, 10, 33, 6, 2, 6, 15, 2, 2, 6, 35, 6, 2, 2, 15, 6, 2, 6, 15, 10, 2, 6, 2, 6, 2 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

a(n) = A123624(n) / n.

From Robert Israel, Apr 02 2017:

If n is squarefree, a(n) is the product of the least two primes coprime to n.

Otherwise a(n) = 2. (End)

LINKS

R. Zumkeller, Table of n, a(n) for n = 1..10000

MAPLE

a:= proc(n) local r, p, count;

  if not numtheory:-issqrfree(n) then return 2 fi;

  r:= 1; count:= 0; p:= 1;

  do

    p:= nextprime(p);

    if n mod p > 0 then

      count:= count+1;

      r:= r*p;

      if count = 2 then return r fi

    fi

  od

end proc:

map(a, [$1..1000]); # Robert Israel, Apr 02 2017

MATHEMATICA

a[n_] := Module[{r = 1, p = 1, count = 0}, If[!SquareFreeQ[n], Return[2]]; While[True, p = NextPrime[p]; If[Mod[n, p] > 0, count++; r = r*p; If[count == 2, Return[r]]]]]; Array[a, 100] (* Jean-François Alcover, Feb 13 2018, after Robert Israel *)

CROSSREFS

Cf. A093316.

Sequence in context: A289722 A070870 A202749 * A240990 A215739 A161397

Adjacent sequences:  A123620 A123621 A123622 * A123624 A123625 A123626

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Oct 03 2006

EXTENSIONS

Name corrected by Robert Israel, Apr 02 2017

STATUS

approved

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Last modified September 28 01:27 EDT 2021. Contains 347698 sequences. (Running on oeis4.)