21728005 has 16 divisors (see below), whose sum is σ = 28224000. Its totient is φ = 15962688.

The previous prime is 21727999. The next prime is 21728009. The reversal of 21728005 is 50082712.

It is a cyclic number.

It is not a de Polignac number, because 21728005 - 2⁹ = 21727493 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21728009) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 13746 + ... + 15244.

It is an arithmetic number, because the mean of its divisors is an integer number (1764000).

Almost surely, 2^21728005 is an apocalyptic number.

It is an amenable number.

21728005 is a deficient number, since it is larger than the sum of its proper divisors (6495995).

21728005 is a wasteful number, since it uses less digits than its factorization.

21728005 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1740.

The product of its (nonzero) digits is 1120, while the sum is 25.

The square root of 21728005 is about 4661.3308185539. The cubic root of 21728005 is about 279.0443825712.

The spelling of 21728005 in words is "twenty-one million, seven hundred twenty-eight thousand, five".