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Tricky sequence

Author: mathforces
Problem has been solved: 28 times

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Let $ a_1, a_2, \dots, a_n $ be an arithmetic progression of integers such that $ a_i $ is divisible by $ i $ for all $ i = 1, 2, \dots, n-1 $ and $ a_n $ is not divisible by $ n $. Find the number of possible values of $ n < 100 $.





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