21728929 has 4 divisors (see below), whose sum is σ = 21745584. Its totient is φ = 21712276.

The previous prime is 21728909. The next prime is 21728939. The reversal of 21728929 is 92982712.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21728929 - 2¹³ = 21720737 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21728891 and 21728900.

It is not an unprimeable number, because it can be changed into a prime (21728909) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 6187 + ... + 9040.

It is an arithmetic number, because the mean of its divisors is an integer number (5436396).

Almost surely, 2^21728929 is an apocalyptic number.

It is an amenable number.

21728929 is a deficient number, since it is larger than the sum of its proper divisors (16655).

21728929 is a wasteful number, since it uses less digits than its factorization.

21728929 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16654.

The product of its digits is 36288, while the sum is 40.

The square root of 21728929 is about 4661.4299308259. The cubic root of 21728929 is about 279.0483380403.

The spelling of 21728929 in words is "twenty-one million, seven hundred twenty-eight thousand, nine hundred twenty-nine".