We have decimal-expansion tag. However, this is probably more suited for decimal expansions of real numbers, not for writing integer in base ten.
I think that the tag number-systems might be used. This tag is also suitable for expansions in other bases. The tag-excerpt for (number-systems) says:
Questions on the different ways to represent a number, how to convert between those different ways, and other such questions. The usual system employed by humans is the decimal (base-10) system, but other systems like binary and hexadecimal are also in frequent use.
This was briefly discussed in chat some time ago, see here.
This and this discussion are also related, to some extent.