820021 has 4 divisors (see below), whose sum is σ = 863200. Its totient is φ = 776844.

The previous prime is 819991. The next prime is 820037. The reversal of 820021 is 120028.

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 820021 - 2⁵ = 819989 is a prime.

It is an Ulam number.

It is a Duffinian number.

820021 is a lucky number.

It is a junction number, because it is equal to n+sod(n) for n = 819983 and 820010.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (820051) 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, 21561 + ... + 21598.

It is an arithmetic number, because the mean of its divisors is an integer number (215800).

2⁸²⁰⁰²¹ is an apocalyptic number.

It is an amenable number.

820021 is a deficient number, since it is larger than the sum of its proper divisors (43179).

820021 is a wasteful number, since it uses less digits than its factorization.

820021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 43178.

The product of its (nonzero) digits is 32, while the sum is 13.

The square root of 820021 is about 905.5501090497. The cubic root of 820021 is about 93.5998152406.

Adding to 820021 its reverse (120028), we get a palindrome (940049).

The spelling of 820021 in words is "eight hundred twenty thousand, twenty-one".