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Proof WritingHardPigeonhole and Extremal Arguments

Pigeonhole and Extremal Arguments · Hard problem

The partial-sum argument for block sums looks at s0=0,s1,s2,…s_0 = 0, s_1, s_2, \ldots modulo nn. For the list 4,9,2,7,5,84, 9, 2, 7, 5, 8, how many blocks of CONSECUTIVE terms have a sum divisible by 66?