21724224 has 28 divisors (see below), whose sum is σ = 57479184. Its totient is φ = 7241344.

The previous prime is 21724207. The next prime is 21724229. The reversal of 21724224 is 42242712.

It is a Harshad number since it is a multiple of its sum of digits (24).

It is a junction number, because it is equal to n+sod(n) for n = 21724194 and 21724203.

It is not an unprimeable number, because it can be changed into a prime (21724229) by changing a digit.

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 3 ways as a sum of consecutive naturals, for example, 56382 + ... + 56765.

It is an arithmetic number, because the mean of its divisors is an integer number (2052828).

Almost surely, 2^21724224 is an apocalyptic number.

21724224 is a gapful number since it is divisible by the number (24) formed by its first and last digit.

It is an amenable number.

21724224 is an abundant number, since it is smaller than the sum of its proper divisors (35754960).

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

21724224 is a wasteful number, since it uses less digits than its factorization.

21724224 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 113162 (or 113152 counting only the distinct ones).

The product of its digits is 1792, while the sum is 24.

The square root of 21724224 is about 4660.9252300375. The cubic root of 21724224 is about 279.0281956577.

Adding to 21724224 its reverse (42242712), we get a palindrome (63966936).

The spelling of 21724224 in words is "twenty-one million, seven hundred twenty-four thousand, two hundred twenty-four".