21723242 has 8 divisors (see below), whose sum is σ = 32656932. Its totient is φ = 10837600.

The previous prime is 21723239. The next prime is 21723253. The reversal of 21723242 is 24232712.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 20421361 + 1301881 = 4519^2 + 1141^2 .

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

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 10859 + ... + 12702.

Almost surely, 2^21723242 is an apocalyptic number.

21723242 is a deficient number, since it is larger than the sum of its proper divisors (10933690).

21723242 is a wasteful number, since it uses less digits than its factorization.

21723242 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 24024.

The product of its digits is 1344, while the sum is 23.

The square root of 21723242 is about 4660.8198849559. The cubic root of 21723242 is about 279.0239912909.

Adding to 21723242 its reverse (24232712), we get a palindrome (45955954).

The spelling of 21723242 in words is "twenty-one million, seven hundred twenty-three thousand, two hundred forty-two".