819821 has 4 divisors (see below), whose sum is σ = 837312. Its totient is φ = 802332.

The previous prime is 819811. The next prime is 819823. The reversal of 819821 is 128918.

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 a de Polignac number, because none of the positive numbers 2^k-819821 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (819823) 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, 8675 + ... + 8768.

It is an arithmetic number, because the mean of its divisors is an integer number (209328).

2⁸¹⁹⁸²¹ is an apocalyptic number.

It is an amenable number.

819821 is a deficient number, since it is larger than the sum of its proper divisors (17491).

819821 is a wasteful number, since it uses less digits than its factorization.

819821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 17490.

The product of its digits is 1152, while the sum is 29.

The square root of 819821 is about 905.4396722035. The cubic root of 819821 is about 93.5922050757.

The spelling of 819821 in words is "eight hundred nineteen thousand, eight hundred twenty-one".