Unable to compute factors p and q from exponent d.

Raise code

                p = gcd(cand + 1, n)
                spotted = True
                break
            k *= 2
        # This value was not any good... let's try another!
        a += 2
    if not spotted:
        raise ValueError("Unable to compute factors p and q from exponent d.")
    # Found !
    q, r = divmod(n, p)
    assert r == 0
    p, q = sorted((p, q), reverse=True)
    return (p, q)