21678720 has 128 divisors (see below), whose sum is σ = 79021440. Its totient is φ = 4952064.

The previous prime is 21678697. The next prime is 21678731. The reversal of 21678720 is 2787612.

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

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 12634 + ... + 14246.

It is an arithmetic number, because the mean of its divisors is an integer number (617355).

Almost surely, 2^21678720 is an apocalyptic number.

21678720 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 21678720, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (39510720).

21678720 is an abundant number, since it is smaller than the sum of its proper divisors (57342720).

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

21678720 is a wasteful number, since it uses less digits than its factorization.

21678720 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1642 (or 1630 counting only the distinct ones).

The product of its (nonzero) digits is 9408, while the sum is 33.

The square root of 21678720 is about 4656.0412369308. The cubic root of 21678720 is about 278.8332401032.

The spelling of 21678720 in words is "twenty-one million, six hundred seventy-eight thousand, seven hundred twenty".