21660224 has 28 divisors (see below), whose sum is σ = 43397424. Its totient is φ = 10725504.

The previous prime is 21660211. The next prime is 21660239. The reversal of 21660224 is 42206612.

It is a hoax number, since the sum of its digits (23) coincides with the sum of the digits of its distinct prime factors.

It is a self number, because there is not a number n which added to its sum of digits gives 21660224.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 5267 + ... + 8429.

It is an arithmetic number, because the mean of its divisors is an integer number (1549908).

Almost surely, 2^21660224 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 21660224, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (21698712).

21660224 is an abundant number, since it is smaller than the sum of its proper divisors (21737200).

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

21660224 is a wasteful number, since it uses less digits than its factorization.

21660224 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3282 (or 3272 counting only the distinct ones).

The product of its (nonzero) digits is 1152, while the sum is 23.

The square root of 21660224 is about 4654.0545763882. The cubic root of 21660224 is about 278.7539185839.

Adding to 21660224 its reverse (42206612), we get a palindrome (63866836).

The spelling of 21660224 in words is "twenty-one million, six hundred sixty thousand, two hundred twenty-four".