An 8x8 grid; 6 token types (letters, numbers, colors etc.). Filling the grid with tokens such that there are no more than two of any token adjacent horizontally or vertically. Ie. 

F F B B C C D D
A B C D E F A B
A B C D E F A B
F E D B C A F E
F F E F F E F F
A B C D A B C D
C D E F C D E F
A A F F A A C C

[download]

Generating one is messy but simple. Enumerating them is considerably harder; and would probably take a very long time.

I'd like to know how many legal patterns there are? But I can't wrap my head around how to calculate it.

Any hints or leads appreciated.

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In reply to Pattern enumeration. by BrowserUk

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