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Find the greatest prime divisor of the sum of the arithmetic sequence

1+2+3+.......+80
 

 Jul 19, 2020
 #1
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Sum up the sequence first using: n * (n+1) / 2 formula:[80 * 81] / 2 =3,240

 

Then factor 3240 = 2^3 * 3^4 * 5

 

As you can see, the largest Prime factor = 5

 Jul 19, 2020

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