21821821 has 8 divisors (see below), whose sum is σ = 25220160. Its totient is φ = 18493728.

The previous prime is 21821819. The next prime is 21821843. The reversal of 21821821 is 12812812.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21821821 - 2¹ = 21821819 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21821221) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 16891 + ... + 18136.

It is an arithmetic number, because the mean of its divisors is an integer number (3152520).

Almost surely, 2^21821821 is an apocalyptic number.

It is an amenable number.

21821821 is a deficient number, since it is larger than the sum of its proper divisors (3398339).

21821821 is an equidigital number, since it uses as much as digits as its factorization.

21821821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 35123.

The product of its digits is 512, while the sum is 25.

The square root of 21821821 is about 4671.3831998670. The cubic root of 21821821 is about 279.4454201580.

Subtracting from 21821821 its reverse (12812812), we obtain a palindrome (9009009).

The spelling of 21821821 in words is "twenty-one million, eight hundred twenty-one thousand, eight hundred twenty-one".