To eliminate page numbers entirely, the simplest method is

\def\thepage{}

To add them back again

\def\thepage{\arabic{page}}

\arabic could also be \Roman or \roman for other numbering styles.

Note that the page counter is also incremented even when
the \thepage is turned off.

If you need to set the page number to a specific value, say 7,
you can

\setcounter{page}{7}