821813 has 4 divisors (see below), whose sum is σ = 857568. Its totient is φ = 786060.

The previous prime is 821809. The next prime is 821819. The reversal of 821813 is 318128.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 821813 - 2² = 821809 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (23), and also a Moran number because the ratio is a prime number: 35731 = 821813 / (8 + 2 + 1 + 8 + 1 + 3).

It is a Duffinian number.

It is a plaindrome in base 15.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (821819) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 17843 + ... + 17888.

It is an arithmetic number, because the mean of its divisors is an integer number (214392).

2⁸²¹⁸¹³ is an apocalyptic number.

It is an amenable number.

821813 is a deficient number, since it is larger than the sum of its proper divisors (35755).

821813 is a wasteful number, since it uses less digits than its factorization.

821813 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 35754.

The product of its digits is 384, while the sum is 23.

The square root of 821813 is about 906.5390228777. The cubic root of 821813 is about 93.6679471688.

The spelling of 821813 in words is "eight hundred twenty-one thousand, eight hundred thirteen".