Level
pending

The answer is 6210001000.

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I started out by saying the number was

0000000000

This has 10 zeros, but when we make the first digit a nine, it has nine zeros.

9000000000

But now there is a nine, so we keep re-writing the problem.

9000000001

8000000001

8000000010

8100000010

7100000010

7200000010

7210000010

7210000100

6210000100

6210001000

And this number works!