I came up with this today: we say a positive integer $k$ is a composiphile if there exists no positive integer $n \leq k$ such that $$\frac{k!}{n} + 1 \text{ is prime.}$$ My question: are there infinitely many composiphiles?
My comments: I have checked up to $k=50$, and have found $18$ to be the only composiphile no greater than $50$. I have tried a proof by contradiction to prove their infinitude, although it got very messy very quickly, and don't see how I might continue.
Update: just my luck, $51$ is also a composiphile, and so is $53$.
Using this self-defined function
we get the following start of the output
I aborted the calculation, hence the list upto 500 need not be complete. But upto 429, exactly the displayed numbers are composiphiles.
Heuristically, we can expect infinite many composiphiles. If $k$ is large, we have $k$ chances to find a prime with magnitude approximately $k!$. It is not a great surprise, if we do not find a prime, hence my guess. Of course, this is not a proof, but I have great doubts anyway that this can be actually proven (or, even more suprisingly , disproven).