ID: 001 GRP:1
.
.
ID:020 GRP:20
ID:021 GRP:1
.
.
ID:120 GRP:20

##</code><code>##

for (my $i = 1; $i < 7; $i++) {
    for (my $g = 1; $g < 21; $g++) {
      my $j = $i * $g;
      my $id = sprintf ("%03d", $j);
      print "ID: $id\t GRP: $g \n";
    }
}