number of element in a principal ideal domain can be $25/36/35/15$? Could any one tell me number of element in a principal ideal domain can be $25/36/35/15$ ?

I just know a principal ideal domain is generated by a single element. what the knowledge I need to find this result?

Thank you
First, you need to know that any finite integral domain is a field. Then you should know that there is a finite field of cardinality $n$ if and only if $n$ is a prime power.

Note that what you said is probably not what you meant:


  a principal ideal domain is generated by a single element.


In any ring $R$, we have that $R$ is equal to the ideal generated by $1_R$, so this is true,  but the statement you probably meant is


  every ideal of a principal ideal domain is generated by a single element.
25 elements can have a principal ideal  domain because for if n is p^2 then there exist a field of order P^2 moreover since a field is pid then every ideal is principal.