21845821 has 4 divisors (see below), whose sum is σ = 21862144. Its totient is φ = 21829500.

The previous prime is 21845809. The next prime is 21845827. The reversal of 21845821 is 12854812.

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 21845821 - 2⁷ = 21845693 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 (21845827) 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, 5955 + ... + 8896.

It is an arithmetic number, because the mean of its divisors is an integer number (5465536).

Almost surely, 2^21845821 is an apocalyptic number.

It is an amenable number.

21845821 is a deficient number, since it is larger than the sum of its proper divisors (16323).

21845821 is a wasteful number, since it uses less digits than its factorization.

21845821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 16322.

The product of its digits is 5120, while the sum is 31.

The square root of 21845821 is about 4673.9513262335. The cubic root of 21845821 is about 279.5478288567.

The spelling of 21845821 in words is "twenty-one million, eight hundred forty-five thousand, eight hundred twenty-one".