A257832 Squarefree numbers that are k*A005117(k) for some k.

1, 30, 42, 70, 165, 247, 330, 442, 570, 805, 1247, 1457, 1749, 1870, 1995, 2183, 2318, 2418, 2706, 2814, 2967, 3358, 3478, 4182, 4505, 4785, 5187, 5394, 5546, 5917, 6262, 7169, 7590, 7770, 8023, 8395, 9471, 9906, 10191, 10906, 11122, 11730, 11954, 12727, 13286, 14043, 15326, 16665, 17201

Offset

1,2

Comments

k*A005117(k) is in the sequence iff k is squarefree and gcd(k,A005117(k)) = 1. - Robert Israel, May 22 2015

Links

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Formula

A005117(m) equal to k*A005117(k).

Example

30 is in this sequence because the 5th squarefree is 6 and 5*6 = 30.

Maple

k:= 0:
count:= 0:
for m from 1 while count < 100 do
  if numtheory:-issqrfree(m) then
     k:= k+1;
     if numtheory:-issqrfree(k) and igcd(k, m)=1 then
       count:= count+1;
       A[count]:= k*m;
     fi
  fi
od:
seq(A[i], i=1..count); # Robert Israel, May 22 2015

Prog

(PARI) list(lim)=my(v=List(), k, t); for(s=1, lim, if(issquarefree(s), t=k++*s; if(t>lim, return(Vec(v))); if(issquarefree(t), listput(v, t)))) \\ Charles R Greathouse IV, May 22 2015

Crossrefs

Cf. A005117.

Sequence in context: A367481 A219742 A348557 * A050776 A268697 A258358

Adjacent sequences: A257829 A257830 A257831 * A257833 A257834 A257835

Keyword

nonn

Author

Juri-Stepan Gerasimov, May 10 2015

Extensions

Name corrected by Robert Israel, May 22 2015

Status

approved