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Let a1,a2,a3,...,an be n numbers such that each ai is either 1 or -1. If a1a2a3a4+a2a3a4a5+...+ana1a2a3=0. Then prove that 4 divides n.
I can't understand the solution provided. Please simplify.
Where is the solution is provided ?
The solution is provided in the Cheenta portal itself.