sub fix{
    my ($n,$m)=@_;
    my $M = $n % $m;
    $M ? $n + $m - $M : $n
}

print "<table width='80%' align='center' border='1'>\n";
print "<tr><th></th><th colspan='4'>\$m</th></tr>\n";
for my $n (0..20) {
    print "  <tr>".join("", map { "<th>$_</th>" } '$n',2..5),"</tr>\n"
        unless $n;
    print "  <tr>".join("", map { "<td>$_</td>" } $n,map fix($n,$_),2..5),"</tr>\n";
}
print "</table>";
__END__