21805051 has 4 divisors (see below), whose sum is σ = 21848400. Its totient is φ = 21761704.

The previous prime is 21805037. The next prime is 21805073. The reversal of 21805051 is 15050812.

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

It is a cyclic number.

It is not a de Polignac number, because 21805051 - 2⁵ = 21805019 is a prime.

It is a super-2 number, since 2×21805051² = 950920498225202, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21805001) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 20911 + ... + 21928.

It is an arithmetic number, because the mean of its divisors is an integer number (5462100).

Almost surely, 2^21805051 is an apocalyptic number.

21805051 is a deficient number, since it is larger than the sum of its proper divisors (43349).

21805051 is an equidigital number, since it uses as much as digits as its factorization.

21805051 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 43348.

The product of its (nonzero) digits is 400, while the sum is 22.

The square root of 21805051 is about 4669.5878833148. The cubic root of 21805051 is about 279.3738175074.

Adding to 21805051 its reverse (15050812), we get a palindrome (36855863).

The spelling of 21805051 in words is "twenty-one million, eight hundred five thousand, fifty-one".