This is Perl module Math::CheckDigits. INSTALLATION Math::CheckDigits installation is straightforward. If your CPAN shell is set up, you should just be able to do % cpan Math::CheckDigits Download it, unpack it, then build it as per the usual: % perl Makefile.PL % make && make test Then install it: % make install DOCUMENTATION Math::CheckDigits documentation is available as in POD. So you can do: % perldoc Math::CheckDigits to read the documentation online with your favorite pager. Songmu