21229920 has 144 divisors (see below), whose sum is σ = 75714912. Its totient is φ = 5406720.

The previous prime is 21229919. The next prime is 21229927. The reversal of 21229920 is 2992212.

It is a tau number, because it is divible by the number of its divisors (144).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21229927) 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 23 ways as a sum of consecutive naturals, for example, 32800 + ... + 33440.

It is an arithmetic number, because the mean of its divisors is an integer number (525798).

Almost surely, 2^21229920 is an apocalyptic number.

21229920 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 21229920, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (37857456).

21229920 is an abundant number, since it is smaller than the sum of its proper divisors (54484992).

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

21229920 is a wasteful number, since it uses less digits than its factorization.

21229920 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 685 (or 674 counting only the distinct ones).

The product of its (nonzero) digits is 1296, while the sum is 27.

The square root of 21229920 is about 4607.5937320905. The cubic root of 21229920 is about 276.8956411566.

The spelling of 21229920 in words is "twenty-one million, two hundred twenty-nine thousand, nine hundred twenty".