809821 has 2 divisors, whose sum is σ = 809822. Its totient is φ = 809820.

The previous prime is 809803. The next prime is 809827. The reversal of 809821 is 128908.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 657721 + 152100 = 811^2 + 390^2 .

It is a cyclic number.

It is not a de Polignac number, because 809821 - 2⁹ = 809309 is a prime.

It is a plaindrome in base 13.

It is a self number, because there is not a number n which added to its sum of digits gives 809821.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (809827) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 404910 + 404911.

It is an arithmetic number, because the mean of its divisors is an integer number (404911).

2⁸⁰⁹⁸²¹ is an apocalyptic number.

It is an amenable number.

809821 is a deficient number, since it is larger than the sum of its proper divisors (1).

809821 is an equidigital number, since it uses as much as digits as its factorization.

809821 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1152, while the sum is 28.

The square root of 809821 is about 899.9005500609. The cubic root of 809821 is about 93.2101080725.

The spelling of 809821 in words is "eight hundred nine thousand, eight hundred twenty-one".