olymmath

Putnam 2022 B4

  • Session B

Find all integers nn with n≥4n \geq 4 for which there exists a sequence of distinct real numbers x1,…,xnx_1,\dots,x_n such that each of the sets

{x1,x2,x3},{x2,x3,x4},…,{xn−2,xn−1,xn},{xn−1,xn,x1}, and {xn,x1,x2}\begin{gathered}\{x_1,x_2,x_3\}, \{x_2,x_3,x_4\}, \dots, \\ \{x_{n-2},x_{n-1},x_n\}, \{x_{n-1},x_n, x_1\}, \text{ and } \{x_n, x_1, x_2\}\end{gathered}

forms a 3-term arithmetic progression when arranged in increasing order.

Curated text Kedlaya Putnam archive. Quoted with source.

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