21680000 has 80 divisors (see below), whose sum is σ = 54170160. Its totient is φ = 8640000.

The previous prime is 21679979. The next prime is 21680003. The reversal of 21680000 is 8612.

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

It is a hoax number, since the sum of its digits (17) coincides with the sum of the digits of its distinct prime factors.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21680003) by changing a digit.

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 9 ways as a sum of consecutive naturals, for example, 79865 + ... + 80135.

It is an arithmetic number, because the mean of its divisors is an integer number (677127).

Almost surely, 2^21680000 is an apocalyptic number.

21680000 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 21680000, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27085080).

21680000 is an abundant number, since it is smaller than the sum of its proper divisors (32490160).

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

21680000 is an frugal number, since it uses more digits than its factorization.

21680000 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 305 (or 278 counting only the distinct ones).

The product of its (nonzero) digits is 96, while the sum is 17.

The square root of 21680000 is about 4656.1786907291. The cubic root of 21680000 is about 278.8387278122.

Adding to 21680000 its reverse (8612), we get a palindrome (21688612).

The spelling of 21680000 in words is "twenty-one million, six hundred eighty thousand".