521821 has 4 divisors (see below), whose sum is σ = 528192. Its totient is φ = 515452.

The previous prime is 521819. The next prime is 521831. The reversal of 521821 is 128125.

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 a cyclic number.

It is not a de Polignac number, because 521821 - 2¹ = 521819 is a prime.

It is a Duffinian number.

521821 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (521831) 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, 3061 + ... + 3226.

It is an arithmetic number, because the mean of its divisors is an integer number (132048).

2⁵²¹⁸²¹ is an apocalyptic number.

It is an amenable number.

521821 is a deficient number, since it is larger than the sum of its proper divisors (6371).

521821 is an equidigital number, since it uses as much as digits as its factorization.

521821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6370.

The product of its digits is 160, while the sum is 19.

The square root of 521821 is about 722.3717879319. The cubic root of 521821 is about 80.5082742932.

Adding to 521821 its reverse (128125), we get a palindrome (649946).

The spelling of 521821 in words is "five hundred twenty-one thousand, eight hundred twenty-one".