On the mod_rewrite page I found the example
RewriteRule ^(.+\.php)s$ $1
which rewrites files with names ending with ".phps" to end instead with ".php" (the idea was that these would then be processed and rendered as syntax-highlighted source code).
So to turn that into what you want, it's a matter of replacing the 's' with "any digit". The most conventional way of doing that would be to write '[0-9]'; as the page also mentions that Apache uses Perl-compatible regexps, it could be written as '\d' instead.