Find the greatest prime divisor of the value of the arithmetic series 1 + 2 + 3 + \dots + 135 + 136 + 137 + 138 + 139 + 140.
Sum = (140) (141) / 2 = = 70 * 141
70 = 2 * 7 * 5
141 = 3 * 47
So
70 * 141 =
(2 * 7 * 5) * ( 3 * 47 )
47 is the greatest prime divisor
+162 
