21509689 has 4 divisors (see below), whose sum is σ = 21874320. Its totient is φ = 21145060.

The previous prime is 21509671. The next prime is 21509701. The reversal of 21509689 is 98690512.

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 21509689 - 2¹⁵ = 21476921 is a prime.

It is a Smith number, since the sum of its digits (40) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21509639) 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, 182227 + ... + 182344.

It is an arithmetic number, because the mean of its divisors is an integer number (5468580).

Almost surely, 2^21509689 is an apocalyptic number.

It is an amenable number.

21509689 is a deficient number, since it is larger than the sum of its proper divisors (364631).

21509689 is an equidigital number, since it uses as much as digits as its factorization.

21509689 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 364630.

The product of its (nonzero) digits is 38880, while the sum is 40.

The square root of 21509689 is about 4637.8539218048. The cubic root of 21509689 is about 278.1066521415.

The spelling of 21509689 in words is "twenty-one million, five hundred nine thousand, six hundred eighty-nine".