21728728 has 32 divisors (see below), whose sum is σ = 47446560. Its totient is φ = 9135360.

The previous prime is 21728719. The next prime is 21728741. The reversal of 21728728 is 82782712.

It is a happy number.

It is a nude number because it is divisible by every one of its digits.

It is a congruent number.

It is an unprimeable number.

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 7 ways as a sum of consecutive naturals, for example, 693 + ... + 6628.

It is an arithmetic number, because the mean of its divisors is an integer number (1482705).

Almost surely, 2^21728728 is an apocalyptic number.

21728728 is a gapful number since it is divisible by the number (28) formed by its first and last digit.

It is an amenable number.

21728728 is an abundant number, since it is smaller than the sum of its proper divisors (25717832).

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

21728728 is a wasteful number, since it uses less digits than its factorization.

21728728 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7387 (or 7383 counting only the distinct ones).

The product of its digits is 25088, while the sum is 37.

The square root of 21728728 is about 4661.4083708682. The cubic root of 21728728 is about 279.0474776069.

The spelling of 21728728 in words is "twenty-one million, seven hundred twenty-eight thousand, seven hundred twenty-eight".