sieve.tex

\documentclass[a4j]{jsarticle}

\makeatletter
\def\eratos#1 {{%
    \newcount \eratos@i \relax
    \eratos@i = 1 \relax
    \@whilenum\eratos@i<#1\do{%
        \@namedef{eratos@isprime\the\eratos@i}{1} \relax
        \advance \eratos@i 1 \relax
    }%

    \@namedef{eratos@isprime2}{1} \relax
    \eratos@i = 2 \relax
    \@whilenum\eratos@i<#1\do{%
        \ifnum\@nameuse{eratos@isprime\the\eratos@i}=1
            \newcount \eratos@j \relax
            \eratos@j = \the\eratos@i \relax
            \advance \eratos@j \eratos@i \relax
            \@whilenum\eratos@j<#1\do{%
                \@namedef{eratos@isprime\the\eratos@j}{0} \relax
                \advance \eratos@j \eratos@i \relax
            }%
        \fi%
        \advance \eratos@i 1 \relax
    }%

    \eratos@i = 2 \relax
    \@whilenum \eratos@i<#1\do{%
        \ifnum\@nameuse{eratos@isprime\the\eratos@i}=1
            \noindent\the\eratos@i\quad
        \fi
        \advance \eratos@i 1 \relax
    }%
}}%
\makeatother

\begin{document}
\eratos{10000}
\end{document}