check for numbers that for conference matrices surely exist

conf_check.c

#include <gmp.h>
#include <stdio.h>
#include <stdlib.h>
#include <math.h>

static int prime_or_power(mpz_t c_1, int log2, mpz_t *rop)
{
        if (mpz_probab_prime_p(c_1, 100) != 0) return 1;
        int i;
        for(i=1; i<log2; i++)
        {
                if (mpz_root(*rop, c_1, i) == 0) continue;
                if(mpz_probab_prime_p(*rop, 100) != 0) return 1;
        }
        return 0;
}

int main(int argc, char **argv)
{
        int from = atoi(argv[1]);
        int to = atoi(argv[2]);
        printf("checking from %d to %d\n", from, to);
        mpz_t c, c_1, rop;
        mpz_inits(c, c_1, rop, 0);
        unsigned int i;
        for(i=from; i<to; i++)
        {
                mpz_set_ui(c, i);
                if(mpz_fdiv_ui(c, 4) != 2) continue;
                mpz_sub_ui(c_1, c, 1);
                if(prime_or_power(c_1, (int)ceil(log2(i)), &rop)  == 0) continue;
                printf("%d\n", i);
        }
        mpz_clears(c, c_1, rop, 0);
        return 0;
}