205921 has 4 divisors (see below), whose sum is σ = 218052. Its totient is φ = 193792.

The previous prime is 205913. The next prime is 205937. The reversal of 205921 is 129502.

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

It can be written as a sum of positive squares in 2 ways, for example, as 112896 + 93025 = 336^2 + 305^2 .

It is a cyclic number.

It is not a de Polignac number, because 205921 - 2³ = 205913 is a prime.

It is a super-3 number, since 3×205921³ = 26195287573334883, which contains 333 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (205951) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 6040 + ... + 6073.

It is an arithmetic number, because the mean of its divisors is an integer number (54513).

2²⁰⁵⁹²¹ is an apocalyptic number.

It is an amenable number.

205921 is a deficient number, since it is larger than the sum of its proper divisors (12131).

205921 is a wasteful number, since it uses less digits than its factorization.

205921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12130.

The product of its (nonzero) digits is 180, while the sum is 19.

The square root of 205921 is about 453.7851914728. The cubic root of 205921 is about 59.0518552058.

It can be divided in two parts, 2059 and 21, that added together give a triangular number (2080 = T₆₄).

The spelling of 205921 in words is "two hundred five thousand, nine hundred twenty-one".