# Square free numbers

• Jun 13th 2009, 01:37 PM
miz.perfect84
Square free numbers
Can anyone help with this problem?
a function is defined to be abundant
• Jun 13th 2009, 06:08 PM
TheAbstractionist
Do you mean find $F(p^{\color{red}r\color{black}})\,?$
• Jun 14th 2009, 02:00 AM
miz.perfect84
yes
yes, sorry, i did type that in word but i think when i copied and pasted it it didn't come out right, thanks for that
• Jun 14th 2009, 03:30 AM
TheAbstractionist
The number of integers between 1 and $p^r$ which are not coprime with $p^r$ are $p,\,p^2,\,p^3,\,\ldots,\,p^r.$ Of these, only $p$ is such that $\gcd(p,p^r)=p$ is square-free. So the integers $1\le a\le p^r$ such that $\gcd(a,p^r)$ is not square-free are the $r-1$ integers $p^2,\,p^3,\,\ldots,\,p^r.$

$\therefore\ F(p^r)=p^r-(r-1)=p^r-r+1.$