Beautiful result on 2-primitive sets! GPT-5.6 just solved another 50+ year old problem (Erdős #793)
GPT-5.6 Sol Ultra found me a solution to another Erdos problem not long after this one. Problem #793 asks about asymptotic of a 2-primitive set. GPT again came up with an extremely short and elegant construction that enhances original Erdos method used to prove a weaker result.