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 ? "=:%d" : "=:%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;     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