Cách 1:
uses crt;
var i,n:longint;
begin
clrscr;
write('Nhap n: ');readln(n);
i:=2;
while (n>1)and(n mod i<>0) do inc(i);
if i=n then writeln('N la so nguyen to') else
writeln('N khong la so nguyen to');
readln
end.
Cách 2:
uses crt;
var i,n,d:longint;
begin
clrscr;
write('Nhap n: ');readln(n);
for i:=1 to n do
if n mod i=0 then inc(d);
if d=2 then writeln('N la so nguyen to') else
writeln('N khong la so nguyen to');
readln
end.