可逆素数

#include <stdio.h>
#include <math.h>
int main()
{
    int i,count;
    printf("There are invertable primrs with 4 digits:\n");
    for(count=0,i=1001; i<9999; i+=2)
      if(num(i))
        printf(count%9 ? "%3d:%d" : "%3d:%d\n",++count,i);


    return 0;
}
int num(int number)
{
    int j,i;
    if(!ok(number))
    return (0);
    for(i=number,j=0;i>0;i/=10)
        j=j*10+i%10;
    if(number<j)
      if(!ok(j))
      return 0;
      else return 1;
    else return 0;
}
int ok(int number)
{
    int i,j;
    if(number%2==0)
    return 0;
    j=sqrt((double)number)+1;
    for(i=3; i<=j; i+=2)
      if(number%i==0)
    return 0;
    return 1;

}

   [root@localhost 32]# vim invertable.c 
[root@localhost 32]# gcc invertable.c -lm
[root@localhost 32]# ./a.out 
There are invertable primrs with 4 digits:
  1:1009  2:1021  3:1031  4:1033  5:1061  6:1069  7:1091  8:1097  9:1103
 10:1109 11:1151 12:1153 13:1181 14:1193 15:1213 16:1217 17:1223 18:1229
 19:1231 20:1237 21:1249 22:1259 23:1279 24:1283 25:1381 26:1399 27:1409
 28:1429 29:1439 30:1453 31:1471 32:1487 33:1499 34:1523 35:1559 36:1583
 37:1597 38:1619 39:1657 40:1669 41:1723 42:1733 43:1753 44:1789 45:1847
 46:1867 47:1879 48:1913 49:1933 50:1949 51:1979 52:3019 53:3023 54:3049
 55:3067 56:3083 57:3089 58:3109 59:3163 60:3169 61:3257 62:3299 63:3319
 64:3343 65:3347 66:3359 67:3373 68:3389 69:3407 70:3463 71:3467 72:3469
 73:3527 74:3583 75:3697 76:3719 77:3767 78:3889 79:3917 80:3929 81:7027
 82:7057 83:7177 84:7187 85:7219 86:7229 87:7297 88:7349 89:7457 90:7459
 91:7529 92:7577 93:7589 94:7649 95:7687 96:7699 97:7879 98:7949 99:9029