21720768 has 112 divisors (see below), whose sum is σ = 61447680. Its totient is φ = 6759424.

The previous prime is 21720749. The next prime is 21720779. The reversal of 21720768 is 86702712.

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, 261655 + ... + 261737.

It is an arithmetic number, because the mean of its divisors is an integer number (548640).

Almost surely, 2^21720768 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21720768, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30723840).

21720768 is an abundant number, since it is smaller than the sum of its proper divisors (39726912).

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

21720768 is a wasteful number, since it uses less digits than its factorization.

21720768 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 174 (or 164 counting only the distinct ones).

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

The square root of 21720768 is about 4660.5544734506. The cubic root of 21720768 is about 279.0133984650.

The spelling of 21720768 in words is "twenty-one million, seven hundred twenty thousand, seven hundred sixty-eight".