2156821 has 4 divisors (see below), whose sum is σ = 2161312. Its totient is φ = 2152332.

The previous prime is 2156813. The next prime is 2156839. The reversal of 2156821 is 1286512.

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 2156821 - 2³ = 2156813 is a prime.

It is a Duffinian number.

2156821 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (2156801) 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, 1425 + ... + 2518.

It is an arithmetic number, because the mean of its divisors is an integer number (540328).

2^2156821 is an apocalyptic number.

It is an amenable number.

2156821 is a deficient number, since it is larger than the sum of its proper divisors (4491).

2156821 is an equidigital number, since it uses as much as digits as its factorization.

2156821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4490.

The product of its digits is 960, while the sum is 25.

The square root of 2156821 is about 1468.6119296805. The cubic root of 2156821 is about 129.2026340813.

The spelling of 2156821 in words is "two million, one hundred fifty-six thousand, eight hundred twenty-one".