20857 has 2 divisors, whose sum is σ = 20858. Its totient is φ = 20856.

The previous prime is 20849. The next prime is 20873. The reversal of 20857 is 75802.

20857 is nontrivially palindromic in base 11.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20736 + 121 = 144^2 + 11^2 .

It is a cyclic number.

It is not a de Polignac number, because 20857 - 2³ = 20849 is a prime.

It is a nialpdrome in base 13.

It is not a weakly prime, because it can be changed into another prime (20807) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10428 + 10429.

It is an arithmetic number, because the mean of its divisors is an integer number (10429).

2²⁰⁸⁵⁷ is an apocalyptic number.

It is an amenable number.

20857 is a deficient number, since it is larger than the sum of its proper divisors (1).

20857 is an equidigital number, since it uses as much as digits as its factorization.

20857 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 560, while the sum is 22.

The square root of 20857 is about 144.4195277655. The cubic root of 20857 is about 27.5264758793.

Multiplying 20857 by its sum of digits (22), we get a palindrome (458854).

Subtracting 20857 from its reverse (75802), we obtain a palindrome (54945).

The spelling of 20857 in words is "twenty thousand, eight hundred fifty-seven".