[aleunix]

Now i'm on OpenBSD so i don't check it but i think you have right.

Now i was thinking at something sufficient general for avoid to use seq or jot that can be work on OpenBSD and Linux without modification of the code.
These attempt failed:

for i in {$1.. $2}
for ((i=$1; i <= $2 ; i++))

so, in the end, now i'm using that approach:
i=$1
while [ "$i" -le $2 ]
do
echo $i
let "i+=1"
done
I haven't check on Linux but given that i make this change while see it:
Example 11-17. C-style syntax in a while loop from the Advanced Bash-Scripting Guide
i suppose that should work.