Online Course Discussion Forum

MCIII Number Theory 4.25

 
 
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Re: MCIII Number Theory 4.25
by Tina Jin - Sunday, 14 January 2024, 11:40 AM
 

I understand now! When n=odd, the sum of ai cannot be even number (namely cannot be 0). When n=even, there must be more than 1 even ai, so n is a multiple of 4 and therefor congruent to 0 mod 4.