Number Theory

 

Find the greatest prime divisor of the value of the arithmetic series    
1 + 2 + 3 + \dots + 200    

 

The sum of this series is (200 / 2)(1 + 200)  =  (100)(201)  =  20,100    

 

The factors of 20,100 are 2². 3, 5², 67     (I admit I looked this up.)    

 

The larges prime divisor of 20,100 is therefore 67.    

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