21223728 has 80 divisors (see below), whose sum is σ = 61846240. Its totient is φ = 6967296.

The previous prime is 21223723. The next prime is 21223739. The reversal of 21223728 is 82732212.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is not an unprimeable number, because it can be changed into a prime (21223723) 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 15 ways as a sum of consecutive naturals, for example, 31200 + ... + 31872.

It is an arithmetic number, because the mean of its divisors is an integer number (773078).

Almost surely, 2^21223728 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 21223728, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30923120).

21223728 is an abundant number, since it is smaller than the sum of its proper divisors (40622512).

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

21223728 is a wasteful number, since it uses less digits than its factorization.

21223728 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 763 (or 751 counting only the distinct ones).

The product of its digits is 2688, while the sum is 27.

The square root of 21223728 is about 4606.9217488471. The cubic root of 21223728 is about 276.8687183902.

The spelling of 21223728 in words is "twenty-one million, two hundred twenty-three thousand, seven hundred twenty-eight".