21728505 has 16 divisors (see below), whose sum is σ = 35337024. Its totient is φ = 11398080.

The previous prime is 21728471. The next prime is 21728513. The reversal of 21728505 is 50582712.

It is not a de Polignac number, because 21728505 - 2⁸ = 21728249 is a prime.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 10959 + ... + 12788.

It is an arithmetic number, because the mean of its divisors is an integer number (2208564).

Almost surely, 2^21728505 is an apocalyptic number.

It is an amenable number.

21728505 is a deficient number, since it is larger than the sum of its proper divisors (13608519).

21728505 is a wasteful number, since it uses less digits than its factorization.

21728505 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 23816.

The product of its (nonzero) digits is 5600, while the sum is 30.

The square root of 21728505 is about 4661.3844509974. The cubic root of 21728505 is about 279.0465229905.

The spelling of 21728505 in words is "twenty-one million, seven hundred twenty-eight thousand, five hundred five".