21724681 has 8 divisors (see below), whose sum is σ = 23918400. Its totient is φ = 19567440.

The previous prime is 21724663. The next prime is 21724721. The reversal of 21724681 is 18642712.

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

It is a cyclic number.

It is not a de Polignac number, because 21724681 - 2⁵ = 21724649 is a prime.

It is a super-2 number, since 2×21724681² = 943923529103522, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21724621) by changing a digit.

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 7 ways as a sum of consecutive naturals, for example, 7861 + ... + 10258.

It is an arithmetic number, because the mean of its divisors is an integer number (2989800).

Almost surely, 2^21724681 is an apocalyptic number.

It is an amenable number.

21724681 is a deficient number, since it is larger than the sum of its proper divisors (2193719).

21724681 is a wasteful number, since it uses less digits than its factorization.

21724681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 18239.

The product of its digits is 5376, while the sum is 31.

The square root of 21724681 is about 4660.9742543807. The cubic root of 21724681 is about 279.0301522292.

The spelling of 21724681 in words is "twenty-one million, seven hundred twenty-four thousand, six hundred eighty-one".