21388729 has 4 divisors (see below), whose sum is σ = 22078720. Its totient is φ = 20698740.

The previous prime is 21388723. The next prime is 21388751. The reversal of 21388729 is 92788312.

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 21388729 - 2³ = 21388721 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21388691 and 21388700.

It is not an unprimeable number, because it can be changed into a prime (21388721) 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, 344949 + ... + 345010.

It is an arithmetic number, because the mean of its divisors is an integer number (5519680).

Almost surely, 2^21388729 is an apocalyptic number.

It is an amenable number.

21388729 is a deficient number, since it is larger than the sum of its proper divisors (689991).

21388729 is an equidigital number, since it uses as much as digits as its factorization.

21388729 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 689990.

The product of its digits is 48384, while the sum is 40.

The square root of 21388729 is about 4624.7950224848. The cubic root of 21388729 is about 277.5843598186.

The spelling of 21388729 in words is "twenty-one million, three hundred eighty-eight thousand, seven hundred twenty-nine".