tail -n 4 somefile.txt > somefile_n.txt
keep rows after a specific number, here four (see https://unix.stackexchange.com/questions/96226/delete-first-line-of-a-file)
tail -n +4 somefile.txt > somefile_minus_n.txt
seq 1 1000 > count.txt
tail -n 4 somefile.txt > somefile_n.txt
tail -n +4 somefile.txt > somefile_minus_n.txt
seq 1 1000 > count.txt