Solution

158484

First name
Dylan
School
Wharncliffe Side Primary school
Country
Age
9

At first I didn't know what the question was telling me to do, so I just guessed.

I thought it would be to add the digits up till seventeen so I did that.

If you had wrote 17 digits the last number you wrote would be 13,
If the last number you wrote was 20 you would of wrote 31 digits.

That is what I think the answer is, but I might be wrong!