57 (fifty-seven) is the natural number following 56 and preceding 58. It is a composite number.
57 is a semiprime, a Blum integer, and a Leyland number.
The split Lie algebra E<sub></sub> has a 57-dimensional Heisenberg algebra as its nilradical, and the smallest possible homogeneous space for E<sub>8</sub> is also 57-dimensional.
Although fifty-seven is not prime, it is jokingly known as the Grothendieck prime after a legend in which the mathematician Alexander Grothendieck gave it as an example of a prime number, not realizing it was divisible by three and nineteen. The same error was made by another famous mathematician, Hermann Weyl, in a published article.