820409 has 2 divisors, whose sum is σ = 820410. Its totient is φ = 820408.

The previous prime is 820399. The next prime is 820411. The reversal of 820409 is 904028.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 760384 + 60025 = 872^2 + 245^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-820409 is a prime.

It is a Sophie Germain prime.

Together with 820411, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (820429) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 410204 + 410205.

It is an arithmetic number, because the mean of its divisors is an integer number (410205).

2⁸²⁰⁴⁰⁹ is an apocalyptic number.

It is an amenable number.

820409 is a deficient number, since it is larger than the sum of its proper divisors (1).

820409 is an equidigital number, since it uses as much as digits as its factorization.

820409 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 576, while the sum is 23.

The square root of 820409 is about 905.7643181314. The cubic root of 820409 is about 93.6145754325.

The spelling of 820409 in words is "eight hundred twenty thousand, four hundred nine".