Generating n Optimally Differentiatable colours

Mr Tufte,

I sometimes have issues with default colours in graphs being too similar to each other to be easily differentiated.

Given a number n (assume between 5 and 25 or so) is there an algorithm to generate a set of RGB colours that are most differentiatable from each other to the human eye? I believe such an algorithm may need to take into account human biology.

I firmly believe research on this subject must have been done and yet I can’t find anything, not even canned lists of 12 optimally differentiatable colours for instance.

Have you come across this problem in your travels?

Thanks in advance,

Paul