21780928 has 56 divisors (see below), whose sum is σ = 47621952. Its totient is φ = 9821184.

The previous prime is 21780923. The next prime is 21780947. The reversal of 21780928 is 82908712.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21780923) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 38826 + ... + 39382.

It is an arithmetic number, because the mean of its divisors is an integer number (850392).

Almost surely, 2^21780928 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 21780928, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (23810976).

21780928 is an abundant number, since it is smaller than the sum of its proper divisors (25841024).

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

21780928 is a wasteful number, since it uses less digits than its factorization.

21780928 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 629 (or 619 counting only the distinct ones).

The product of its (nonzero) digits is 16128, while the sum is 37.

The square root of 21780928 is about 4667.0041782711. The cubic root of 21780928 is about 279.2707554328.

The spelling of 21780928 in words is "twenty-one million, seven hundred eighty thousand, nine hundred twenty-eight".