21808640 has 80 divisors (see below), whose sum is σ = 59808672. Its totient is φ = 7471104.

The previous prime is 21808621. The next prime is 21808681. The reversal of 21808640 is 4680812.

It is a tau number, because it is divible by the number of its divisors (80).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 17312 + ... + 18528.

Almost surely, 2^21808640 is an apocalyptic number.

21808640 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 21808640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29904336).

21808640 is an abundant number, since it is smaller than the sum of its proper divisors (38000032).

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

21808640 is an equidigital number, since it uses as much as digits as its factorization.

21808640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1247 (or 1231 counting only the distinct ones).

The product of its (nonzero) digits is 3072, while the sum is 29.

The square root of 21808640 is about 4669.9721626579. The cubic root of 21808640 is about 279.3891445009.

The spelling of 21808640 in words is "twenty-one million, eight hundred eight thousand, six hundred forty".