21731023 has 4 divisors (see below), whose sum is σ = 21763800. Its totient is φ = 21698248.

The previous prime is 21730991. The next prime is 21731029. The reversal of 21731023 is 32013712.

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 21731023 - 2⁵ = 21730991 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 (21731029) 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, 15373 + ... + 16726.

It is an arithmetic number, because the mean of its divisors is an integer number (5440950).

Almost surely, 2^21731023 is an apocalyptic number.

21731023 is a deficient number, since it is larger than the sum of its proper divisors (32777).

21731023 is an equidigital number, since it uses as much as digits as its factorization.

21731023 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 32776.

The product of its (nonzero) digits is 252, while the sum is 19.

The square root of 21731023 is about 4661.6545346046. The cubic root of 21731023 is about 279.0573016428.

Adding to 21731023 its reverse (32013712), we get a palindrome (53744735).

The spelling of 21731023 in words is "twenty-one million, seven hundred thirty-one thousand, twenty-three".