821128921 has 4 divisors (see below), whose sum is σ = 821363200. Its totient is φ = 820894644.

The previous prime is 821128907. The next prime is 821128933. The reversal of 821128921 is 129821128.

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 821128921 - 2⁷ = 821128793 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (821120921) 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, 111801 + ... + 118918.

It is an arithmetic number, because the mean of its divisors is an integer number (205340800).

Almost surely, 2^821128921 is an apocalyptic number.

It is an amenable number.

821128921 is a deficient number, since it is larger than the sum of its proper divisors (234279).

821128921 is a wasteful number, since it uses less digits than its factorization.

821128921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 234278.

The product of its digits is 4608, while the sum is 34.

The square root of 821128921 is about 28655.3471624407. The cubic root of 821128921 is about 936.4195015044.

The spelling of 821128921 in words is "eight hundred twenty-one million, one hundred twenty-eight thousand, nine hundred twenty-one".