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No Monochrome Sums (Posted on 2009-10-14) Difficulty: 3 of 5
Color each of the numbers 1 through n either red or blue such that if a+b=c then a, b and c are not all the same color. The addends are distinct.

For example with n=6 the sequence rbrbrb does not work because 2+4=6 but are all blue. Whereas rbrbbr does work.

What is the largest value of n for which such a sequence exists?

Note: Since the colors can be swapped, make the number 1 red.

Add a third color (green.) What is the new maximum value of n?

See The Solution Submitted by Jer    
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Greens to the Party | Comment 3 of 10 |
By expanding the color palate to Red, Blue, and Green, and again starting with N=9, there are 3150 distinct solutions, the lowest of which is R R B R B B R G G.  Perhaps Jer intended some interpretation for N > 9 (e.g. add ABCDEF and look for distinct hexadecimal solutions) but this is not apparent to me from the wording.  The same strategy/coding would work, but with more equations to test.
  Posted by ed bottemiller on 2009-10-14 15:13:59
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