Sounds more like the field is a code than a number. Just because something has only numeric characters doesn't mean it is actually numeric. My master card account # is 16 numeric characters but isn't actually a "number".
If parts of a field mean something, then they shouldn't be mushed together.
arnel's solution is fine for what you asked. Just be aware the it precludes the use of any index so if your table is large, the query could be clunky.