c# - Find prime using square root -

here question,

find sum of primes below 2 million.

my code lists many non-primes such 9,15..., wrong?

using system; using system.collections.generic; using system.diagnostics; using system.linq; using system.text; using system.threading.tasks;  namespace p10 {     // sum of primes below 10 2 + 3 + 5 + 7 = 17. find sum of primes below 2 million.     class program     {         static list<long> list = new list<long>();         static void main(string[] args)         {             stopwatch sw = stopwatch.startnew();             list.add(2);             list.add(3);             long x = list.last();             while (x < 2000000)             {                 x += 2;                 findprime(x);             }             long y = list.sum() - list.last();             console.writeline(y);             console.writeline("time used (float): {0} ms", sw.elapsed.totalmilliseconds);             console.writeline("time used (rounded): {0} ms", sw.elapsedmilliseconds);             console.readkey();         }          static void findprime(int64 p)         {             int64 max = (int64)math.ceiling(math.sqrt(p));             foreach (long n in list)             {                 while (n <= max)                 {                     if (p / n == 0)                     {                         continue;                     }                     else                     {                         list.add(p);                         break;                     }                 }break;             }         }     } } 

when testing if 1 number divisible another, want know if remainder zero. change this:

if (p / n == 0) 

to this:

if (p % n == 0) 

but still looks there issues loop. can rewrite as:

static void findprime(long p) {     long max = (long)math.ceiling(math.sqrt(p));     foreach (long n in list)     {         if (n > max)          {             break;         }         else if (p % n == 0)         {             return;         }     }      list.add(p); }