You don't need the gamma function to get to 7. You can stay at an Algebra 1 level.
I solved the puzzle for 1-10 before looking at the answers, and this was my solution for 7:
⌊√222⌋/2
or more readably:
floor(sqrt(222)) / 2
I solved the puzzle for 1-10 before looking at the answers, and this was my solution for 7:
⌊√222⌋/2
or more readably:
floor(sqrt(222)) / 2
ceil(2.2)+2+2