21724138 has 8 divisors (see below), whose sum is σ = 32741280. Its totient is φ = 10810380.

The previous prime is 21724133. The next prime is 21724139. The reversal of 21724138 is 83142712.

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

It is not an unprimeable number, because it can be changed into a prime (21724133) 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, 25318 + ... + 26161.

It is an arithmetic number, because the mean of its divisors is an integer number (4092660).

Almost surely, 2^21724138 is an apocalyptic number.

21724138 is a deficient number, since it is larger than the sum of its proper divisors (11017142).

21724138 is a wasteful number, since it uses less digits than its factorization.

21724138 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 51692.

The product of its digits is 2688, while the sum is 28.

The square root of 21724138 is about 4660.9160043923. The cubic root of 21724138 is about 279.0278274595.

The spelling of 21724138 in words is "twenty-one million, seven hundred twenty-four thousand, one hundred thirty-eight".