I have an outcome (O) which could have three states: octal 4, octal 2 or octal 1.

With three such outcomes I have 27 combinations.

The challenge is to find an algorithm which gives me the minimum number of combinations (NK) which always gives me minimum 2 of 3 states correct.

An example: The combinations 4-4-4 covers the following combinations: 4-4-4, 4-4-2, 4-2-4, 2-4-4, 4-4-1, 4-1-4, 1-4-4 given this requirement.

Mathematically this could be done with only 4 combinations, but how do I find them ???

(The total challenge covers 2-3 states and up til 12 outcomes).