205125821 has 4 divisors (see below), whose sum is σ = 205575132. Its totient is φ = 204676512.

The previous prime is 205125773. The next prime is 205125827. The reversal of 205125821 is 128521502.

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 181980100 + 23145721 = 13490^2 + 4811^2 .

It is a cyclic number.

It is not a de Polignac number, because 205125821 - 2¹⁸ = 204863677 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (205125827) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 223970 + ... + 224883.

It is an arithmetic number, because the mean of its divisors is an integer number (51393783).

Almost surely, 2^205125821 is an apocalyptic number.

It is an amenable number.

205125821 is a deficient number, since it is larger than the sum of its proper divisors (449311).

205125821 is an equidigital number, since it uses as much as digits as its factorization.

205125821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 449310.

The product of its (nonzero) digits is 1600, while the sum is 26.

The square root of 205125821 is about 14322.2142492004. The cubic root of 205125821 is about 589.7574613560.

It can be divided in two parts, 2051 and 25821, that added together give a palindrome (27872).

The spelling of 205125821 in words is "two hundred five million, one hundred twenty-five thousand, eight hundred twenty-one".