Find nine different integers from 1 to 20 inclusive such that no combination of any three of the nine integers form an arithmetic sequence.
(For example, if two of the integers chosen were 7 and 13, then that would preclude 1, 10 and 19 from being included.)
(In reply to Counting Up
Such a progression seems to yield only 8 integers:
1,2, 4,5, 10,11, 13,14
the next number that avoids an arithmetic sequence is 28.
Posted by Jer
on 2013-04-08 16:01:02