Currently the form's numeric entry response feature don't allow for much control.
For example, the character count or numerical range can't be specified.
Also, any entry response specified as numeric that is >999 is automatically formatted with comma separators so that the entry "234567" is displayed as "234,567".
Lastly, a numeric response leading with a single or multiple 0's will not display those same numeric characters.
Specifying a "string" response of numeric characters as a "short answer" is a workaround, but it still allows for input error.