Somehow I am getting 171
All the lines that can be drawn with 21 points = 21C2 =
Number of sides = 21
So number of diagonals when diagonals are drawn from all edges = 210 - 21 = 189 (Subtract the number of sides)
Number of missing diagonals when one of the vertex does not have any diagonals= 21-3 = 18 (By drawing some of the known polygons... you can see n-3 disgonals will be missing)
Total = 189-18 = 171
"To dream anything that you want to dream, that is the beauty of the human mind. To do anything that you want to do, that is the strength of the human will. To trust yourself, to test your limits, that is the courage to succeed."
- Bernard Edmonds