johngg@abouriou ~/perl/Monks $ perl -Mstrict -Mwarnings -E '
say for
   map {
       my $w = $_;
       my $x = $w + 1;
       map {
           my $y = $_ + 1;
           map {
               my $z = $_ + 1;
               map {
                   join q{}, $w, $x, $y, $z
               } $z .. 9
           } $y .. 8
       } $x .. 7
    } 0 .. 6;' | wc -l
210