21243723 has 4 divisors (see below), whose sum is σ = 28324968. Its totient is φ = 14162480.

The previous prime is 21243721. The next prime is 21243731. The reversal of 21243723 is 32734212.

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 21243723 - 2¹ = 21243721 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21243693 and 21243702.

It is not an unprimeable number, because it can be changed into a prime (21243721) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3540618 + ... + 3540623.

It is an arithmetic number, because the mean of its divisors is an integer number (7081242).

Almost surely, 2^21243723 is an apocalyptic number.

21243723 is a deficient number, since it is larger than the sum of its proper divisors (7081245).

21243723 is an equidigital number, since it uses as much as digits as its factorization.

21243723 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7081244.

The product of its digits is 2016, while the sum is 24.

The square root of 21243723 is about 4609.0913421194. The cubic root of 21243723 is about 276.9556376540.

Adding to 21243723 its reverse (32734212), we get a palindrome (53977935).

The spelling of 21243723 in words is "twenty-one million, two hundred forty-three thousand, seven hundred twenty-three".