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Correct answer: 31
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Let Then and since is one-one, are all distinct.
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The given condition is i.e. Rearranging,
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Since , we have Also because codomain is .
So we must count ordered triples of distinct elements from such that and then set with the additional requirement that is distinct from .
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Because of the coefficient , we must have small values of .
Case 1:
Then with distinctness requiring distinct, so and . Also .
Now count ordered pairs with , , and
For each :
- : , with and gives values.
- : , from excluding gives values.
- : , from excluding gives values.
- : , from gives values.
- : no solution.
Total so far:
But we must also ensure .
- impossible since .
- would mean , impossible.
- would mean , impossible.
So all are valid.
Case 2:
Then Distinctness requires , . Also
Now cannot be ? It can be, since only distinct from and . So count ordered pairs with , , , and .
For each :
- : , excluding gives values.
- : , excluding gives values.
- : , possible only, so value.
- : no solution.
So tentative total:
Now check .
- impossible since .
- gives , impossible.
- gives , impossible.
Hence all are valid.
Case 3:
Then so Also , .
Count ordered pairs:
- : , from excluding gives values.
- : , from excluding gives value.
- : no solution.
Tentative total:
Check .
- impossible.
- impossible.
- would imply , impossible.
So all are valid.
Case 4:
Then Since , But if , then . Since must be distinct and neither can equal , only possibility is or . Let us check:
- gives , valid and distinct.
- gives , not allowed.
So for , there is exactly solution.
If , then so no solution.
Thus Case 4 contributes .
- Total number of one-one functions is
Therefore, the required number is
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