[~] $ perl -e'($x,$y)=@ARGV;do{$z.=$x}while`whois $y$z.com`!~
              /No m/;print"$y$z"' x|wc -c
     64
[download]

Yes, that's right, someone bothered to register all of /x{1,63}\.com/.

Other fun:

[~] $ perl -le'($x,$y)=@ARGV;do{$z.=$x}while`whois $y$z.com`!~
               /No m/;print"$y$z"' o m
mooooooooo
[download]