Find the greatest prime divisor of the value of the arithmetic series 1 + 2 + 3 + \dots + 135 + 136 + 137 + 138 + 139 + 140.
You can use Guass Formula to find the sum from 1 through n .
(n+1)*n/2=141*140/2=141*70
Since we want to find the prime factors:
141=3*47
70=7*2*5
SO we need the greatest which is \(\left [ 47 \right ]\)
+760 
