818821 has 2 divisors, whose sum is σ = 818822. Its totient is φ = 818820.

The previous prime is 818819. The next prime is 818827. The reversal of 818821 is 128818.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 504100 + 314721 = 710^2 + 561^2 .

It is a cyclic number.

It is not a de Polignac number, because 818821 - 2¹ = 818819 is a prime.

It is a super-4 number, since 4×818821⁴ (a number of 25 digits) contains 4444 as substring.

Together with 818819, it forms a pair of twin primes.

It is a self number, because there is not a number n which added to its sum of digits gives 818821.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (818827) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 409410 + 409411.

It is an arithmetic number, because the mean of its divisors is an integer number (409411).

2⁸¹⁸⁸²¹ is an apocalyptic number.

It is an amenable number.

818821 is a deficient number, since it is larger than the sum of its proper divisors (1).

818821 is an equidigital number, since it uses as much as digits as its factorization.

818821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1024, while the sum is 28.

The square root of 818821 is about 904.8872857986. The cubic root of 818821 is about 93.5541356740.

The spelling of 818821 in words is "eight hundred eighteen thousand, eight hundred twenty-one".