@futurebird I think the only composite number<60 AND no common factors with 60
51 is 3x17 (shares 3)
53 is prime, not composite
55 shares 5
57 shares 3 again
59 is prime
So I could imagine that Babylonian/Sumerian mathematicians might think of 49 as the "most prime-y composite, with a secret key associated with the first difficult number number (7)"