21497724 has 72 divisors (see below), whose sum is σ = 59714928. Its totient is φ = 6739200.

The previous prime is 21497699. The next prime is 21497731. The reversal of 21497724 is 42779412.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 15874 + ... + 17174.

It is an arithmetic number, because the mean of its divisors is an integer number (829374).

Almost surely, 2^21497724 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21497724, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29857464).

21497724 is an abundant number, since it is smaller than the sum of its proper divisors (38217204).

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

21497724 is a wasteful number, since it uses less digits than its factorization.

21497724 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1337 (or 1323 counting only the distinct ones).

The product of its digits is 28224, while the sum is 36.

The square root of 21497724 is about 4636.5638138604. The cubic root of 21497724 is about 278.0550759537.

The spelling of 21497724 in words is "twenty-one million, four hundred ninety-seven thousand, seven hundred twenty-four".