• 57 can be written using four 4's:
57 has 4 divisors (see below), whose sum is σ = 80. Its totient is φ = 36.
The previous prime is 53. The next prime is 59. The reversal of 57 is 75.
57 is nontrivially palindromic in base 5 and base 7.
57 is an esthetic number in base 4, base 5 and base 13, because in such bases its adjacent digits differ by 1.
It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.
It is not a de Polignac number, because 57 - 22 = 53 is a prime.
It is a Leyland number of the form 52 + 25.
57 is an idoneal number.
It is an Ulam number.
It is a D-number.
It is the 8-th Hogben number.
It is a Duffinian number.
57 is an undulating number in base 5.
57 is a nontrivial repdigit in base 7.
It is a plaindrome in base 6, base 7, base 10, base 12, base 13, base 15 and base 16.
It is a nialpdrome in base 4, base 7, base 8, base 9, base 11 and base 14.
It is a zygodrome in base 7.
It is a panconsummate number.
It is a nontrivial repunit in base 7.
It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 7 + ... + 12.
It is equal to the Eulerian number A(6, 1).
It is an arithmetic number, because the mean of its divisors is an integer number (20).
It is a Proth number, since it is equal to 7 ⋅ 23 + 1 and 7 < 23.
It is an amenable number.
57 is a deficient number, since it is larger than the sum of its proper divisors (23).
57 is a wasteful number, since it uses less digits than its factorization.
57 is an evil number, because the sum of its binary digits is even.
The sum of its prime factors is 22.
The product of its digits is 35, while the sum is 12.
The square root of 57 is about 7.5498344353. The cubic root of 57 is about 3.8485011313.
Subtracting from 57 its sum of digits (12), we obtain a triangular number (45 = T9).
Subtracting from 57 its product of digits (35), we obtain a palindrome (22).
The spelling of 57 in words is "fifty-seven", and thus it is an aban number, an oban number, and an uban number.
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