21749728 has 144 divisors (see below), whose sum is σ = 59122224. Its totient is φ = 7741440.

The previous prime is 21749723. The next prime is 21749729. The reversal of 21749728 is 82794712.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21749723) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 224176 + ... + 224272.

It is an arithmetic number, because the mean of its divisors is an integer number (410571).

Almost surely, 2^21749728 is an apocalyptic number.

21749728 is a gapful number since it is divisible by the number (28) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21749728, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29561112).

21749728 is an abundant number, since it is smaller than the sum of its proper divisors (37372496).

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

21749728 is a wasteful number, since it uses less digits than its factorization.

21749728 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 145 (or 130 counting only the distinct ones).

The product of its digits is 56448, while the sum is 40.

The square root of 21749728 is about 4663.6603649923. The cubic root of 21749728 is about 279.1373449662.

The spelling of 21749728 in words is "twenty-one million, seven hundred forty-nine thousand, seven hundred twenty-eight".