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(2): Counting Up
There is something to be said for Bryan's method. I've been trying to work it into a problem for the past week - independently of this problem.
I've not considered how Compact a set of n integers can be with no 3 in arithmetic sequence. But I can see by scanning your list that C(9)=20.
It looks like C(7)=13 and C(8) = 14 etc but I'm not sure enough about what your program is doing to know if the first line of solution are minimums.
EDIT: I could have looked it up myself. http://oeis.org/A065825
Edited on April 9, 2013, 12:49 am
Posted by Jer
on 2013-04-09 00:46:52