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Prime-numbering pages

Run the following through TeX and it will page-number with primes. 


\pageno=2

\newcount\p \newcount\q \newcount\flag

\def\advancepageno{
    \loop
        \global\advance\pageno by 1 \p=1
        {\loop
            \advance\p by 1
            \q=\pageno \divide\q by \p \multiply\q by \p
            \ifnum\q=\pageno
               \global\flag=0
            \else
               \global\flag=1
               \q=\p \multiply\q by \p
            \fi
         \ifnum\q<\pageno \repeat}
    \ifnum\flag=0\repeat}


% Now some dummy content.

\loop
    \centerline{This is page \the\pageno} \vfil\eject
\ifnum\pageno<100\repeat

\end

This is not a good program, algorithmically or stylistically, it is just a very simple example of TeX as a programming language.