21518720 has 32 divisors (see below), whose sum is σ = 51444720. Its totient is φ = 8607232.

The previous prime is 21518713. The next prime is 21518723. The reversal of 21518720 is 2781512.

It is a tau number, because it is divible by the number of its divisors (32).

It is a self number, because there is not a number n which added to its sum of digits gives 21518720.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21518723) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 16172 + ... + 17451.

Almost surely, 2^21518720 is an apocalyptic number.

21518720 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21518720 is an abundant number, since it is smaller than the sum of its proper divisors (29926000).

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

21518720 is an equidigital number, since it uses as much as digits as its factorization.

21518720 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 33642 (or 33630 counting only the distinct ones).

The product of its (nonzero) digits is 1120, while the sum is 26.

The square root of 21518720 is about 4638.8274380494. The cubic root of 21518720 is about 278.1455683985.

The spelling of 21518720 in words is "twenty-one million, five hundred eighteen thousand, seven hundred twenty".