21728405 has 8 divisors (see below), whose sum is σ = 26109600. Its totient is φ = 17359056.

The previous prime is 21728393. The next prime is 21728407. The reversal of 21728405 is 50482712.

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 21728405 - 2⁸ = 21728149 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21728407) 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, 1766 + ... + 6824.

It is an arithmetic number, because the mean of its divisors is an integer number (3263700).

Almost surely, 2^21728405 is an apocalyptic number.

It is an amenable number.

21728405 is a deficient number, since it is larger than the sum of its proper divisors (4381195).

21728405 is an equidigital number, since it uses as much as digits as its factorization.

21728405 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5923.

The product of its (nonzero) digits is 4480, while the sum is 29.

The square root of 21728405 is about 4661.3737245580. The cubic root of 21728405 is about 279.0460949093.

The spelling of 21728405 in words is "twenty-one million, seven hundred twenty-eight thousand, four hundred five".