Most likely a calculator is your best bet for odd numbers.
There are many common squares and many common square roots, such as :
1 squared =1
2 squared =4
3 squared = 9
4 squared =16
5 squared = 25
6 squared = 36 and so on...
same with square roots
root 25 is equal to 5
root 16 is equal to 4
root 9 is equal to 3
root 4 is equal to 2
and so on however not every number works out that way so a calculator is often your best bet to find the exact value