255821 has 4 divisors (see below), whose sum is σ = 261312. Its totient is φ = 250332.

The previous prime is 255803. The next prime is 255839. The reversal of 255821 is 128552.

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 an interprime number because it is at equal distance from previous prime (255803) and next prime (255839).

It is a cyclic number.

It is not a de Polignac number, because 255821 - 2⁶ = 255757 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (255841) 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, 2675 + ... + 2768.

It is an arithmetic number, because the mean of its divisors is an integer number (65328).

2²⁵⁵⁸²¹ is an apocalyptic number.

It is an amenable number.

255821 is a deficient number, since it is larger than the sum of its proper divisors (5491).

255821 is an equidigital number, since it uses as much as digits as its factorization.

255821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5490.

The product of its digits is 800, while the sum is 23.

The square root of 255821 is about 505.7875047883. The cubic root of 255821 is about 63.4812394204.

The spelling of 255821 in words is "two hundred fifty-five thousand, eight hundred twenty-one".