820921 has 2 divisors, whose sum is σ = 820922. Its totient is φ = 820920.

The previous prime is 820909. The next prime is 820927. The reversal of 820921 is 129028.

820921 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 608400 + 212521 = 780^2 + 461^2 .

It is a cyclic number.

It is not a de Polignac number, because 820921 - 2⁷ = 820793 is a prime.

It is a super-2 number, since 2×820921² = 1347822576482, which contains 22 as substring.

It is a Chen prime.

820921 is a lucky number.

It is a junction number, because it is equal to n+sod(n) for n = 820892 and 820901.

It is not a weakly prime, because it can be changed into another prime (820927) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 410460 + 410461.

It is an arithmetic number, because the mean of its divisors is an integer number (410461).

2⁸²⁰⁹²¹ is an apocalyptic number.

It is an amenable number.

820921 is a deficient number, since it is larger than the sum of its proper divisors (1).

820921 is an equidigital number, since it uses as much as digits as its factorization.

820921 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 288, while the sum is 22.

The square root of 820921 is about 906.0469082779. The cubic root of 820921 is about 93.6340456785.

Adding to 820921 its reverse (129028), we get a palindrome (949949).

The spelling of 820921 in words is "eight hundred twenty thousand, nine hundred twenty-one".