21731223 has 4 divisors (see below), whose sum is σ = 28974968. Its totient is φ = 14487480.

The previous prime is 21731191. The next prime is 21731239. The reversal of 21731223 is 32213712.

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

It is not a de Polignac number, because 21731223 - 2⁵ = 21731191 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 21731223.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21731243) 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, 3621868 + ... + 3621873.

It is an arithmetic number, because the mean of its divisors is an integer number (7243742).

Almost surely, 2^21731223 is an apocalyptic number.

21731223 is a deficient number, since it is larger than the sum of its proper divisors (7243745).

21731223 is an equidigital number, since it uses as much as digits as its factorization.

21731223 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7243744.

The product of its digits is 504, while the sum is 21.

The square root of 21731223 is about 4661.6759861663. The cubic root of 21731223 is about 279.0581577352.

Adding to 21731223 its reverse (32213712), we get a palindrome (53944935).

The spelling of 21731223 in words is "twenty-one million, seven hundred thirty-one thousand, two hundred twenty-three".