21685760 has 80 divisors (see below), whose sum is σ = 53474256. Its totient is φ = 8429568.

The previous prime is 21685751. The next prime is 21685787. The reversal of 21685760 is 6758612.

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

It is a self number, because there is not a number n which added to its sum of digits gives 21685760.

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, 109982 + ... + 110178.

Almost surely, 2^21685760 is an apocalyptic number.

21685760 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 21685760, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26737128).

21685760 is an abundant number, since it is smaller than the sum of its proper divisors (31788496).

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

21685760 is an equidigital number, since it uses as much as digits as its factorization.

21685760 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 263 (or 247 counting only the distinct ones).

The product of its (nonzero) digits is 20160, while the sum is 35.

The square root of 21685760 is about 4656.7971826138. The cubic root of 21685760 is about 278.8634198303.

The spelling of 21685760 in words is "twenty-one million, six hundred eighty-five thousand, seven hundred sixty".