Start with a set of numbers,

, and find all the subsets of a given size. For example, {1, 2, 3, 4} has six subsets of size 2: {1, 2}, {1, 3}, {1, 4], {2, 3}, {2, 4}, and {3, 4}. Consider {1, 2}—it shares 2 values with itself, 1 value with {1, 3}, and 0 values with {3, 4}. An array of the amount of intersection shows an interesting pattern.