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How many integers n, with 2≤n≤80, is ((n-1(n)(n+1))/8 equal to an integer?

 Oct 16, 2018
 #1
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listfor(n, 2, 80, (n*(n-1)*(n+1)) mod 8
=(6, 0, 4, 0, 2, 0, 0, 0, 6, 0, 4, 0, 2, 0, 0, 0, 6, 0, 4, 0, 2, 0, 0, 0, 6, 0, 4, 0, 2, 0, 0, 0, 6, 0, 4, 0, 2, 0, 0, 0, 6, 0, 4, 0, 2, 0, 0, 0, 6, 0, 4, 0, 2, 0, 0, 0, 6, 0, 4, 0, 2, 0, 0, 0, 6, 0, 4, 0, 2, 0, 0, 0, 6, 0, 4, 0, 2, 0, 0). 

Note: Count ALL the zeros, and that is your answer!!!.                                   

 Oct 16, 2018
 #2
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+1

thank you

thess  Oct 16, 2018

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