Move a range of numbered files?
Since you said it's not always exactly 21 files than you need to move the files manually, and to do that effectively you could use brace expansion:
mv filename{001..21} dir1
mv filename{022..53} dir2
...
Since you said it's not always exactly 21 files than you need to move the files manually, and to do that effectively you could use brace expansion:
mv filename{001..21} dir1
mv filename{022..53} dir2
...