21968256 has 64 divisors (see below), whose sum is σ = 61444800. Its totient is φ = 6935040.

The previous prime is 21968239. The next prime is 21968257. The reversal of 21968256 is 65286912.

It is a tau number, because it is divible by the number of its divisors (64).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21968257) 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 7 ways as a sum of consecutive naturals, for example, 5791 + ... + 8801.

It is an arithmetic number, because the mean of its divisors is an integer number (960075).

Almost surely, 2^21968256 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 21968256, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30722400).

21968256 is an abundant number, since it is smaller than the sum of its proper divisors (39476544).

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

21968256 is a wasteful number, since it uses less digits than its factorization.

21968256 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3047 (or 3035 counting only the distinct ones).

The product of its digits is 51840, while the sum is 39.

The square root of 21968256 is about 4687.0306164991. The cubic root of 21968256 is about 280.0690985927.

The spelling of 21968256 in words is "twenty-one million, nine hundred sixty-eight thousand, two hundred fifty-six".