It's the recursion that makes it clear.
FindAll(3,10) == FindAll(2,9)+FindAll(2,8)+FindAll(2,7)+FindAll(2,6)+etc
======XX==========1XX===========2XX============3XX=========4XX========5XX===6XX===7XX==...

Not a kata issue, you passed all tests until your code timed out. It's a problem with your code not being fast enough to pass all the tests (hint: the part where you check for primality can be improved).