I didn't bother to reverse enginer my email to discover my required activity to become legendary (is that a public algorithm, btw?)...
Yes it's public, but there is a secret seed that isn't, and without this secret seed you can't compute the activity treshold.
(This secret seed is the same for everybody AFAIK)
https://bitcointalk.org/index.php?topic=237597.msg8298386#msg8298386(I can't quote the post because Cloudfare detects the SQL command and blocks the post)