If the length of the perpendicular drawn from the point \( P(a,4,2), a>0 \) on the line \( \displaystyle\frac{x+1}{2}=\frac{y-3}{3}=\frac{z-1}{-1} \) is \( 2\sqrt{6} \) units and \( Q(\alpha_1,\alpha_2,\alpha_3) \) is the image of the point \( P \) in this line, then \( a + \displaystyle\sum_{i=1}^{3}\alpha_i \) is equal to: