21988728 has 48 divisors (see below), whose sum is σ = 61612200. Its totient is φ = 7076160.

The previous prime is 21988721. The next prime is 21988739. The reversal of 21988728 is 82788912.

It is a happy number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21988721) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 3178 + ... + 7353.

Almost surely, 2^21988728 is an apocalyptic number.

It is an amenable number.

21988728 is an abundant number, since it is smaller than the sum of its proper divisors (39623472).

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

21988728 is a wasteful number, since it uses less digits than its factorization.

21988728 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10572 (or 10565 counting only the distinct ones).

The product of its digits is 129024, while the sum is 45.

The square root of 21988728 is about 4689.2140066327. The cubic root of 21988728 is about 280.1560694547.

The spelling of 21988728 in words is "twenty-one million, nine hundred eighty-eight thousand, seven hundred twenty-eight".