솟수 고하는 C프로그램에서 sqrt()함수를 못찾네요..

#include <stdio.h>
#include <math.h>
int is_prime(int n);
main()
{
    int n;
    printf("\nEnter the number : ");
    scanf("%d", &amp;n);
        if (is_prime(n) == 0)
            printf("\n  --> the digit, %d is not a prime number!\n", n);
        else
                printf("\n  --> the digit, %d is a prime number!\n", n);
}
int is_prime(int n)
{
        int i;
        if (n == 2)
                return 1;
        if (n % 2 == 0)
                return 0;
        for (i = 3; i < (int)sqrt(n); i = i + 2)
                if (n % i == 0)
                       return 0;
        return 1;
}
--------------------------------------------------------------------------------------------------------------------------------------------------------
에러메시지
$ gcc prime.c
/tmp/ccAldoMJ.o: In function `is_prime':
prime.c:(.text+0x106): undefined reference to `sqrt'
collect2: ld returned 1 exit status
$

SQRT(3)                    Linux Programmer's Manual                   SQRT(3)
 
 
 
NAME
       sqrt, sqrtf, sqrtl - square root function
 
SYNOPSIS
       #include <math.h>
 
       double sqrt(double x);
       float sqrtf(float x);
       long double sqrtl(long double x);
 
       Link with -lm.
 
DESCRIPTION
       The  sqrt()  function  returns  the  non-negative square root of x.  It
       fails and sets errno to EDOM, if x is negative.
 
ERRORS
       EDOM   x is negative.
 
CONFORMING TO
       SVID 3, POSIX, 4.3BSD, ISO 9899.  The float and the long  double  vari-
       ants are C99 requirements.
 
SEE ALSO
       cbrt(3), csqrt(3), hypot(3)