• No, it's not. It's divisible by 3. (and 19)
  • No, it's not a prime number. Don't you know what 3 times 19 is?
    • beaker95
      Is it 42....?
  • 57 has an aliquot sum of 23 and is the first composite member of the 23-aliquot tree. Although 57 is not prime, it is jokingly known as the "Grothendieck prime" after a story in which mathematician Alexander Grothendieck supposedly gave it as an example of a particular prime number.

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