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 re: Counting Up by Jer)

Of course you're right.  I did OK spotting the arithmetic progressions, but apparently forgot how to count to 9.

Posted by Bryan on 2013-04-09 10:37:33