# Numbers with Distinct Digits

Discrete Mathematics Level pending

Find number of all possible positive integers $$n$$ in decimal presentation satisfying the conditions:

• The leftmost digit of $$n$$ is non-zero, and

• Every digit in $$n$$ occurs at most once within $$n$$.


Clarification:122 is not to be counted. The digit 2 in 122 occurs twice within 122.

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