[ Decimal numeral system ]

A natural number had the sum of its digits subtracted from it, resulting in 2007. What could the original number have been?
It is not difficult to verify that the desired number must be a four-digit number. Let it be $\overline{a b c d}$ $=1000 a+100 b+10 c+d$. Then $1000 a+100 b+10 c+d-(a+b+c+d)=999 a+99 b+9 c=9(111 a+11 b+c)$. We obtain the equation: $9(111 a+11 b+c)=2007 \Leftrightarrow 111 a+11 b+c=223$. By enumeration, we can see that $a>1$ and $a<3$, that is, $a=2$. Then $11 b+c=1$. Since $b$ and $c$ are digits, $b=0$ and $c=1$. Note that $d$ can be any digit.

## Answer

any natural number from 2010 to 2019.