Wouter Meussen wrote: > Note that n must be even in order to realise the 'blackness' of the > complementary blue star. > This means that, in my opinion, the least prime factor for the 'difficult' > cases must be 2. No > special cases for 3*5*7 for instance. Is this a difficult case for 3*5*7? 10 14 21 25 40 42 55 56 63 77 84 85 98 100