21687680 has 128 divisors (see below), whose sum is σ = 61102080. Its totient is φ = 7206912.

The previous prime is 21687641. The next prime is 21687691. The reversal of 21687680 is 8678612.

It is a tau number, because it is divible by the number of its divisors (128).

It is a congruent number.

It is an unprimeable number.

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 15 ways as a sum of consecutive naturals, for example, 210509 + ... + 210611.

It is an arithmetic number, because the mean of its divisors is an integer number (477360).

Almost surely, 2^21687680 is an apocalyptic number.

21687680 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 21687680, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30551040).

21687680 is an abundant number, since it is smaller than the sum of its proper divisors (39414400).

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

21687680 is a wasteful number, since it uses less digits than its factorization.

21687680 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 176 (or 164 counting only the distinct ones).

The product of its (nonzero) digits is 32256, while the sum is 38.

The square root of 21687680 is about 4657.0033283218. The cubic root of 21687680 is about 278.8716495313.

The spelling of 21687680 in words is "twenty-one million, six hundred eighty-seven thousand, six hundred eighty".