21728649 has 8 divisors (see below), whose sum is σ = 28994112. Its totient is φ = 14474480.

The previous prime is 21728633. The next prime is 21728659. The reversal of 21728649 is 94682712.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21728649 - 2⁴ = 21728633 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21728659) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 4084 + ... + 7754.

It is an arithmetic number, because the mean of its divisors is an integer number (3624264).

Almost surely, 2^21728649 is an apocalyptic number.

It is an amenable number.

21728649 is a deficient number, since it is larger than the sum of its proper divisors (7265463).

21728649 is a wasteful number, since it uses less digits than its factorization.

21728649 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5647.

The product of its digits is 48384, while the sum is 39.

The square root of 21728649 is about 4661.3998970266. The cubic root of 21728649 is about 279.0471394251.

The spelling of 21728649 in words is "twenty-one million, seven hundred twenty-eight thousand, six hundred forty-nine".