21728718 has 24 divisors (see below), whose sum is σ = 51359256. Its totient is φ = 6584400.

The previous prime is 21728699. The next prime is 21728719. The reversal of 21728718 is 81782712.

It is a happy number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21728719) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 54673 + ... + 55068.

It is an arithmetic number, because the mean of its divisors is an integer number (2139969).

Almost surely, 2^21728718 is an apocalyptic number.

21728718 is an abundant number, since it is smaller than the sum of its proper divisors (29630538).

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

21728718 is a wasteful number, since it uses less digits than its factorization.

21728718 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 109760 (or 109757 counting only the distinct ones).

The product of its digits is 12544, while the sum is 36.

The square root of 21728718 is about 4661.4072982309. The cubic root of 21728718 is about 279.0474347991.

The spelling of 21728718 in words is "twenty-one million, seven hundred twenty-eight thousand, seven hundred eighteen".