I have had an incredible number of questions about his cache- even after it was found.
I thought Google would provide the explanation for those of us (like me) who are not math majors. 7i in mathematics is the product of all positive integers less than or equal to a given positive integer and denoted by that integer and an exclamation point. Thus, factorial seven is written 7!, meaning 1 × 2 × 3 × 4 × 5 × 6 × 7.
You will need to bring your own pencil or pen to sign the log.
Please do not post any clues to how you found it in your logs.
Congratulations to h2o z for being the First To Find 7!