Error C2064: term does not evaluate to a function taking 1 arguments - C (СИ)

#include <stdafx.h>
#include <stdio.h>
#include <math.h>
#include <stdlib.h>
#include <conio.h>
 
//--------------------------------------------------------------
bool prostoe (int a)
{
    bool res=true;
     int i;
    for (i=1; i<=(int)(sqrt(4.0)(a)); i++) 
        if (a % i == 0)
     {
         res = false;
         break;
     }
    return true;
}
//--------------------------------------------------------------
int main()
{
     const int maxn = 100;
     unsigned short int a[maxn];
     int n,j;
     printf("n = ");
     scanf("%d",&n);
     a[0] = 2;
     a[1] = 3;
     int i;
     for (i = 2; i<=n; i++)
     {
        j = a[i-1] + 2;
        while (!prostoe(j))
           j+= 2;
        a[i] = j;
     getch();
     }
}