21297920 has 72 divisors (see below), whose sum is σ = 58327584. Its totient is φ = 7299072.

The previous prime is 21297907. The next prime is 21297929. The reversal of 21297920 is 2979212.

It is a Harshad number since it is a multiple of its sum of digits (32).

It is not an unprimeable number, because it can be changed into a prime (21297929) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 7772 + ... + 10148.

Almost surely, 2^21297920 is an apocalyptic number.

21297920 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 21297920, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29163792).

21297920 is an abundant number, since it is smaller than the sum of its proper divisors (37029664).

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

21297920 is an equidigital number, since it uses as much as digits as its factorization.

21297920 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2405 (or 2391 counting only the distinct ones).

The product of its (nonzero) digits is 4536, while the sum is 32.

The square root of 21297920 is about 4614.9669554613. The cubic root of 21297920 is about 277.1909607831.

The spelling of 21297920 in words is "twenty-one million, two hundred ninety-seven thousand, nine hundred twenty".