Which of the following functions from Z $->$ R are partial functions, rather than total functions?

Multiple select question.

f$($n$)=1/($n$2+1)$

f$($n$)=$ n$21$

f$($n$)=1/($n$21)$

f$($n$)=$ n$2+1$

f$($n$)=$ n$2$