OFFSET
1,1
COMMENTS
If n is in the sequence, so is m*n. - Charles R Greathouse IV, Oct 16 2015
The asymptotic density of this sequence is 1 - (6/Pi^2) * (1 + Sum_{p prime} (1/p^2 + 1/(p^3*(p+1)) + 1/(p^4*(p+1)))) = 0.07033321843992718294... . - Amiram Eldar, Sep 25 2022
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
FORMULA
A046951(a(n)) > 3.
a(n) < 17n for n > 25. - Charles R Greathouse IV, Oct 16 2015
EXAMPLE
n=200 has 4 square divisors: 1, 4, 25 and 100, therefore 200 is a term.
MATHEMATICA
Select[Range[1000], Length[Rest[Select[ Divisors[#], IntegerQ[ Sqrt[ #]]&]]]> 2&] (* Harvey P. Dale, Jan 08 2014 *)
PROG
(PARI) is(n)=my(f=vecsort(factor(n)[, 2], , 4)); #f && (f[1]>5 || (#f>1 && f[2]>1)) \\ Charles R Greathouse IV, Oct 16 2015
CROSSREFS
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, Apr 08 2003
STATUS
approved