821521 has 4 divisors (see below), whose sum is σ = 832000. Its totient is φ = 811044.

The previous prime is 821519. The next prime is 821551. The reversal of 821521 is 125128.

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 821521 - 2¹ = 821519 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (821551) 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, 5121 + ... + 5278.

It is an arithmetic number, because the mean of its divisors is an integer number (208000).

2⁸²¹⁵²¹ is an apocalyptic number.

It is an amenable number.

821521 is a deficient number, since it is larger than the sum of its proper divisors (10479).

821521 is a wasteful number, since it uses less digits than its factorization.

821521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10478.

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

The square root of 821521 is about 906.3779564839. The cubic root of 821521 is about 93.6568520735.

Adding to 821521 its reverse (125128), we get a palindrome (946649).

The spelling of 821521 in words is "eight hundred twenty-one thousand, five hundred twenty-one".