2105821 has 4 divisors (see below), whose sum is σ = 2109852. Its totient is φ = 2101792.

The previous prime is 2105819. The next prime is 2105833. The reversal of 2105821 is 1285012.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 980100 + 1125721 = 990^2 + 1061^2 .

It is a cyclic number.

It is not a de Polignac number, because 2105821 - 2¹ = 2105819 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 (2105881) 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, 1090 + ... + 2323.

It is an arithmetic number, because the mean of its divisors is an integer number (527463).

2^2105821 is an apocalyptic number.

It is an amenable number.

2105821 is a deficient number, since it is larger than the sum of its proper divisors (4031).

2105821 is an equidigital number, since it uses as much as digits as its factorization.

2105821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4030.

The product of its (nonzero) digits is 160, while the sum is 19.

The square root of 2105821 is about 1451.1447205568. The cubic root of 2105821 is about 128.1761287910.

It can be divided in two parts, 2105 and 821, that added together give a triangular number (2926 = T₇₆).

The spelling of 2105821 in words is "two million, one hundred five thousand, eight hundred twenty-one".