21109729 has 4 divisors (see below), whose sum is σ = 21790720. Its totient is φ = 20428740.

The previous prime is 21109727. The next prime is 21109763. The reversal of 21109729 is 92790112.

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 21109729 - 2¹ = 21109727 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (31), and also a Moran number because the ratio is a prime number: 680959 = 21109729 / (2 + 1 + 1 + 0 + 9 + 7 + 2 + 9).

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21109729.

It is not an unprimeable number, because it can be changed into a prime (21109727) 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 3 ways as a sum of consecutive naturals, for example, 340449 + ... + 340510.

It is an arithmetic number, because the mean of its divisors is an integer number (5447680).

Almost surely, 2^21109729 is an apocalyptic number.

It is an amenable number.

21109729 is a deficient number, since it is larger than the sum of its proper divisors (680991).

21109729 is an equidigital number, since it uses as much as digits as its factorization.

21109729 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 680990.

The product of its (nonzero) digits is 2268, while the sum is 31.

The square root of 21109729 is about 4594.5325115837. The cubic root of 21109729 is about 276.3721132498.

The spelling of 21109729 in words is "twenty-one million, one hundred nine thousand, seven hundred twenty-nine".