If \( \int_{0}^{1} (x^{21} + x^{14} + x^{7}) (2x^{14} + 3x^{7} + 6)^{1/7} \, dx = \frac{1}{l} (11)^{m/n} \) where \( l, m, n \in \mathbb{N} \), \( m \) and \( n \) are coprime then \( l + m + n \) is equal to _______.