21331680 has 96 divisors (see below), whose sum is σ = 70761600. Its totient is φ = 5386752.

The previous prime is 21331679. The next prime is 21331693. The reversal of 21331680 is 8613312.

It is a tau number, because it is divible by the number of its divisors (96).

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

It is a self number, because there is not a number n which added to its sum of digits gives 21331680.

It is a congruent number.

It is an unprimeable number.

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 15 ways as a sum of consecutive naturals, for example, 7951 + ... + 10289.

It is an arithmetic number, because the mean of its divisors is an integer number (737100).

Almost surely, 2^21331680 is an apocalyptic number.

21331680 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21331680, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (35380800).

21331680 is an abundant number, since it is smaller than the sum of its proper divisors (49429920).

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

21331680 is a wasteful number, since it uses less digits than its factorization.

21331680 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2376 (or 2368 counting only the distinct ones).

The product of its (nonzero) digits is 864, while the sum is 24.

The square root of 21331680 is about 4618.6231714657. The cubic root of 21331680 is about 277.3373448220.

Adding to 21331680 its reverse (8613312), we get a palindrome (29944992).

The spelling of 21331680 in words is "twenty-one million, three hundred thirty-one thousand, six hundred eighty".