olymmath

Putnam 2003 B2

  • Session B

Let nn be a positive integer. Starting with the sequence 1,12,13,…,1n1, \frac{1}{2}, \frac{1}{3}, \dots, \frac{1}{n}, form a new sequence of n−1n-1 entries 34,512,…,2n−12n(n−1)\frac{3}{4}, \frac{5}{12}, \dots, \frac{2n-1}{2n(n-1)} by taking the averages of two consecutive entries in the first sequence. Repeat the averaging of neighbors on the second sequence to obtain a third sequence of n−2n-2 entries, and continue until the final sequence produced consists of a single number xnx_n. Show that xn<2/nx_n < 2/n.

Curated text Kedlaya Putnam archive. Quoted with source.

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