20557 has 4 divisors (see below), whose sum is σ = 20956. Its totient is φ = 20160.

The previous prime is 20551. The next prime is 20563. The reversal of 20557 is 75502.

It is a happy number.

It is a semiprime because it is the product of two primes.

It is an interprime number because it is at equal distance from previous prime (20551) and next prime (20563).

It can be written as a sum of positive squares in 2 ways, for example, as 2601 + 17956 = 51^2 + 134^2 .

It is a cyclic number.

It is not a de Polignac number, because 20557 - 2³ = 20549 is a prime.

It is a Duffinian number.

It is a plaindrome in base 11.

It is a nialpdrome in base 12.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20551) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 108 + ... + 229.

It is an arithmetic number, because the mean of its divisors is an integer number (5239).

2²⁰⁵⁵⁷ is an apocalyptic number.

It is an amenable number.

20557 is a deficient number, since it is larger than the sum of its proper divisors (399).

20557 is an equidigital number, since it uses as much as digits as its factorization.

20557 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 398.

The product of its (nonzero) digits is 350, while the sum is 19.

The square root of 20557 is about 143.3771250932. The cubic root of 20557 is about 27.3938608442.

Subtracting 20557 from its reverse (75502), we obtain a palindrome (54945).

It can be divided in two parts, 205 and 57, that added together give a palindrome (262).

The spelling of 20557 in words is "twenty thousand, five hundred fifty-seven".