2091821 has 4 divisors (see below), whose sum is σ = 2140512. Its totient is φ = 2043132.

The previous prime is 2091809. The next prime is 2091839. The reversal of 2091821 is 1281902.

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-2091821 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (2091851) 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, 24281 + ... + 24366.

It is an arithmetic number, because the mean of its divisors is an integer number (535128).

2^2091821 is an apocalyptic number.

It is an amenable number.

2091821 is a deficient number, since it is larger than the sum of its proper divisors (48691).

2091821 is an equidigital number, since it uses as much as digits as its factorization.

2091821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 48690.

The product of its (nonzero) digits is 288, while the sum is 23.

The square root of 2091821 is about 1446.3128983730. The cubic root of 2091821 is about 127.8914484953.

The spelling of 2091821 in words is "two million, ninety-one thousand, eight hundred twenty-one".