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Putnam 1964 B5

Source: Putnam 1964

March 5, 2022
Putnamleast common multipleConvergence

Problem Statement

Let unu_n denote the least common multiple of the first nn terms of a strictly increasing sequence of positive integers. Prove that the series ∑n=1∞1un\sum_{n=1}^{\infty} \frac{1}{ u_n } is convergent
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