2021821 has 4 divisors (see below), whose sum is σ = 2026944. Its totient is φ = 2016700.

The previous prime is 2021807. The next prime is 2021837. The reversal of 2021821 is 1281202.

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 2021821 - 2⁷ = 2021693 is a prime.

It is an Ulam number.

It is a Duffinian number.

2021821 is a lucky number.

It is a junction number, because it is equal to n+sod(n) for n = 2021795 and 2021804.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (2021801) 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, 1915 + ... + 2776.

It is an arithmetic number, because the mean of its divisors is an integer number (506736).

2^2021821 is an apocalyptic number.

It is an amenable number.

2021821 is a deficient number, since it is larger than the sum of its proper divisors (5123).

2021821 is an equidigital number, since it uses as much as digits as its factorization.

2021821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5122.

The product of its (nonzero) digits is 64, while the sum is 16.

The square root of 2021821 is about 1421.9075216061. The cubic root of 2021821 is about 126.4486608630.

The spelling of 2021821 in words is "two million, twenty-one thousand, eight hundred twenty-one".