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Find the greatest prime divisor of the value of the arithmetic series
1 + 2 + 3 + \dots + 135 + 136 + 137 + 138 + 139 + 140.

 Jul 24, 2024
 #1
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take the first and last number. sum them 

140+1=141

 

multiply by half the number of total numbers. 140/2=70

 

we thus have 14170=9870

 

prime factorize 9870. 9870=235747

 

take largest prime number --> 47

 

47 is the answer. 

 Jul 24, 2024
edited by BRAINBOLT  Jul 24, 2024

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