Permutations & Combinations · Counting strictly increasing functions

The number of strictly increasing functions

f

from the set

\{1, 2, 3, 4, 5, 6\}

to the set

\{1, 2, 3, \ldots, 9\}

such that

f(i) \neq i

for

1 \le i \le 6

, is equal to:

We corrected a printing error in the original paper

Source printed the second set as “ $(1, 2, 3, \ldots, 9)$ ” (parentheses instead of set braces).

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