Function is_primitive_root

test/utils/math.hpp:20–26

}

bool is_primitive_root(int m, int g) {
    assert(1 <= g && g < m);
    for (int x : factors(m - 1)) {
        if (atcoder::internal::pow_mod_constexpr(g, (m - 1) / x, m) == 1) return false;
    }
    return true;
}