Let the vertex \( A \) of a triangle \( ABC \) be \( (1, 2) \), and the mid-point of the side \( AB \) be \( (5, -1) \). If the centroid of this triangle is \( (3, 4) \) and its circumcenter is \( (\alpha, \beta) \), then \( 21(\alpha + \beta) \) is equal to:
