809921 has 6 divisors (see below), whose sum is σ = 942210. Its totient is φ = 694176.

The previous prime is 809917. The next prime is 809929. The reversal of 809921 is 129908.

809921 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It can be written as a sum of positive squares in only one way, i.e., 790321 + 19600 = 889^2 + 140^2 .

It is not a de Polignac number, because 809921 - 2² = 809917 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (809929) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 8216 + ... + 8313.

It is an arithmetic number, because the mean of its divisors is an integer number (157035).

2⁸⁰⁹⁹²¹ is an apocalyptic number.

It is an amenable number.

809921 is a deficient number, since it is larger than the sum of its proper divisors (132289).

809921 is a wasteful number, since it uses less digits than its factorization.

809921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16543 (or 16536 counting only the distinct ones).

The product of its (nonzero) digits is 1296, while the sum is 29.

The square root of 809921 is about 899.9561100409. The cubic root of 809921 is about 93.2139445694.

It can be divided in two parts, 80 and 9921, that added together give a palindrome (10001).

The spelling of 809921 in words is "eight hundred nine thousand, nine hundred twenty-one".