21830821 has 4 divisors (see below), whose sum is σ = 21848832. Its totient is φ = 21812812.

The previous prime is 21830803. The next prime is 21830843. The reversal of 21830821 is 12803812.

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-21830821 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 (21830801) 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, 7045 + ... + 9658.

It is an arithmetic number, because the mean of its divisors is an integer number (5462208).

Almost surely, 2^21830821 is an apocalyptic number.

It is an amenable number.

21830821 is a deficient number, since it is larger than the sum of its proper divisors (18011).

21830821 is a wasteful number, since it uses less digits than its factorization.

21830821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 18010.

The product of its (nonzero) digits is 768, while the sum is 25.

The square root of 21830821 is about 4672.3464126710. The cubic root of 21830821 is about 279.4838322152.

The spelling of 21830821 in words is "twenty-one million, eight hundred thirty thousand, eight hundred twenty-one".