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Jun 16th, 2019
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  1.  
  2. int Prime(unsigned long a)
  3. {
  4.    unsigned long i1, i2, i3, i4, i5, i6, i7, i8, bound;
  5.    if (a == 0 || a == 1)
  6.       return 0;
  7.    if (a == 2 || a == 3 || a == 5 || a == 7 || a == 11 || a == 13 || a == 17 || a == 19 || a == 23 || a == 29)
  8.       return 1;
  9.    if (a%2 == 0 || a%3 == 0 || a%5 == 0 || a%7 == 0 || a%11 == 0 || a%13 == 0 || a%17 == 0 || a%19 == 0 || a%23 == 0 || a%29 == 0)
  10.       return 0;
  11.    bound = sqrt((double)a);
  12.    i1 = 31; i2 = 37; i3 = 41; i4 = 43; i5 = 47; i6 = 49; i7 = 53; i8 = 59;
  13.    while (i8 <= bound && a%i1 && a%i2 && a%i3 && a%i4 && a%i5 && a%i6 && a%i7 && a%i8)
  14.    {
  15.        i1 += 30; i2 += 30; i3 += 30; i4 += 30; i5 += 30; i6 += 30; i7 += 30; i8 += 30;
  16.    }
  17.    if (i8 <= bound ||
  18.       i1 <= bound && a % i1 == 0 ||
  19.       i2 <= bound && a % i2 == 0 ||
  20.       i3 <= bound && a % i3 == 0 ||
  21.       i4 <= bound && a % i4 == 0 ||
  22.       i5 <= bound && a % i5 == 0 ||
  23.       i6 <= bound && a % i6 == 0 ||
  24.       i7 <= bound && a % i7 == 0)
  25.          return 0;
  26.    return 1;
  27. }
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