How many strictly ascending 6-digit sequences are there, as $024579$ or $135789$, but not $011234$?
I have tried $10\cdot9\cdot8\cdot7\cdot6\cdot5 =151200$, but this is wrong.
[Math] Number of six-digit numbers with strictly ascending digits.
combinatorics
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Best Answer
Here's another hint: such a number is determined entirely by which numbers are present and which ones are absent. So in order to determine one of these numbers, then, out of the $10$ digits that exist, you simply need to choose $6$ to be present (and the remaining $4$ will be absent).
Now can you come up with a guess for how many six-digit numbers with strictly ascending digits there are? Your first guess is likely to be correct.