21299928 has 64 divisors (see below), whose sum is σ = 57788640. Its totient is φ = 6503424.

The previous prime is 21299923. The next prime is 21299947. The reversal of 21299928 is 82999212.

It is a happy number.

It is a self number, because there is not a number n which added to its sum of digits gives 21299928.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21299923) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 72550 + ... + 72842.

Almost surely, 2^21299928 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 21299928, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28894320).

21299928 is an abundant number, since it is smaller than the sum of its proper divisors (36488712).

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

21299928 is a wasteful number, since it uses less digits than its factorization.

21299928 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 548 (or 544 counting only the distinct ones).

The product of its digits is 46656, while the sum is 42.

The square root of 21299928 is about 4615.1845033541. The cubic root of 21299928 is about 277.1996718365.

The spelling of 21299928 in words is "twenty-one million, two hundred ninety-nine thousand, nine hundred twenty-eight".