int
main(int argc, char *argv[])
{
int *prs, pr_len;
int rv, i, num, is_cp;
int ncircular;
/* get primes below target */
rv = primes_under(TARGET_MAX, &prs, &pr_len);
if (rv)
errx(1, "fail primes_under");
/* find circular prime */
ncircular = 0;
for (i = 0; i < pr_len; i++) {
is_cp = 1;
num = rotation(prs[i]);
while (num != prs[i]) {
if (search(num, prs, pr_len) < 0) {
/* rotation numbe is not prime */
is_cp = 0;
break;
}
num = rotation(num);
}
if (is_cp)
ncircular++;
}
printf("%d\n", ncircular);
return 0;
}
int
main(int argc, char *argv[])
{
int *pr_arr, pr_len, n_found;
int max = 1; /* max number of prime search. this grows '*10' */
int i, tmp;
long sum;
n_found = 0;
sum = 0L;
tmp = 4; /* for skip 2,3,5,7 */
while (1) {
/* we grow search range to 10,100,1000.. */
max *= 10;
if (primes_under(max, &pr_arr, &pr_len))
errx(1, "fail primes_under(%d)", max);
for (i = tmp; i < pr_len; i++) {
if (special(pr_arr[i], pr_arr, pr_len)) {
sum += pr_arr[i];
n_found++;
if (n_found == NEED_NFOUND)
break; /* out to for-loop */
}
}
if (n_found == NEED_NFOUND)
break; /* out to while-loop */
tmp = pr_len; /* skip already checked for next loop */
free(pr_arr);
}
printf("%ld\n", sum);
return 0;
}
int main (int argc, char ** argv) {
if (argc != 2) {
fprintf (stderr, "usage: %s <N>\n", argv[0]);
return 1;
}
int N = atoi (argv[1]);
if (N <= 4) {
printf ("0\n");
return 0;
}
int max_factor = (N - 1) / 2;
size_t primes_count = 0;
int * primes = primes_under (NULL, max_factor + 1, &primes_count);
int count = 0;
for (size_t i = 0; i < primes_count; i++) {
int largest_factor = (N - 1) / primes[i];
if (largest_factor < primes[i])
break;
size_t pi = find_largest_prime (primes, i, primes_count - 1, largest_factor);
count += pi - i + 1;
}
printf ("%d\n", count);
free (primes);
return 0;
}
int
main(int argc, char *argv[])
{
int a, b, c;
int *primes, nprime;
int rv;
/* get all primes under 10000 */
rv = primes_under(10000, &primes, &nprime);
if (rv)
errx(1, "fail primes_under()");
/* skip primes under 1000 */
for (a = 0; primes[a] < 1000; a++);
for (; a < nprime; a++) {
for (b = a + 1; b < nprime; b++) {
c = primes[b] + (primes[b] - primes[a]);
if (search(c, primes, nprime) == -1) {
/* if c is not prime, skip it */
continue;
}
if (same_digs(primes[a], primes[b]) &&
same_digs(primes[b], c)) {
if (primes[a] != 1487)
/* found answer, go out */
goto out;
}
}
}
out:
printf("%d%d%d\n", primes[a], primes[b], c);
free(primes); /* free prime array at heap */
return 0;
}
