21105723 has 8 divisors (see below), whose sum is σ = 28327936. Its totient is φ = 13977000.

The previous prime is 21105709. The next prime is 21105739. The reversal of 21105723 is 32750112.

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

It is not a de Polignac number, because 21105723 - 2⁶ = 21105659 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21105723.

It is not an unprimeable number, because it can be changed into a prime (21105703) 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, 22843 + ... + 23748.

It is an arithmetic number, because the mean of its divisors is an integer number (3540992).

Almost surely, 2^21105723 is an apocalyptic number.

21105723 is a deficient number, since it is larger than the sum of its proper divisors (7222213).

21105723 is a wasteful number, since it uses less digits than its factorization.

21105723 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 46745.

The product of its (nonzero) digits is 420, while the sum is 21.

The square root of 21105723 is about 4594.0965379495. The cubic root of 21105723 is about 276.3546297358.

Adding to 21105723 its reverse (32750112), we get a palindrome (53855835).

The spelling of 21105723 in words is "twenty-one million, one hundred five thousand, seven hundred twenty-three".