Determine whether f is a function from $\mathbb{Z}$ to $\mathbb{R}$.
Enter "Y" for yes and "N" for no.

 1. $f(n)= 1/(n^2+6)$
 2. $f(n)= \frac{1}{n^2-4}$
 3. $f(n)= \sqrt{n^2 +2}$
 4. $f(n)= \pm n$