21724518 has 8 divisors (see below), whose sum is σ = 43449048. Its totient is φ = 7241504.

The previous prime is 21724517. The next prime is 21724519. The reversal of 21724518 is 81542712.

It is an interprime number because it is at equal distance from previous prime (21724517) and next prime (21724519).

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

21724518 is an admirable number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21724517) 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, 1810371 + ... + 1810382.

It is an arithmetic number, because the mean of its divisors is an integer number (5431131).

Almost surely, 2^21724518 is an apocalyptic number.

21724518 is a primitive abundant number, since it is smaller than the sum of its proper divisors, none of which is abundant.

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21724518 is a wasteful number, since it uses less digits than its factorization.

21724518 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3620758.

The product of its digits is 4480, while the sum is 30.

The square root of 21724518 is about 4660.9567687332. The cubic root of 21724518 is about 279.0294543742.

The spelling of 21724518 in words is "twenty-one million, seven hundred twenty-four thousand, five hundred eighteen".