Mathematical and Physical Journal
for High Schools
Issued by the MATFUND Foundation
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# Problem A. 669. (April 2016)

A. 669. Determine whether the set of rational numbers can be ordered to in a sequence $\displaystyle q_1,q_2,\ldots$ in such a way that there is no sequence of indices $\displaystyle 1\le i_1<i_2<\dots<i_6$ such that $\displaystyle q_{i_1},q_{i_2},\ldots,q_{i_6}$ form an arithmetic progression.

Proposed by: Gyula Károlyi, Budajenő and Péter Komjáth, Budapest

(5 pont)

Deadline expired on May 10, 2016.

### Statistics:

 1 student sent a solution. 2 points: 1 student.

Problems in Mathematics of KöMaL, April 2016