21056609 has 4 divisors (see below), whose sum is σ = 24064704. Its totient is φ = 18048516.

The previous prime is 21056597. The next prime is 21056653. The reversal of 21056609 is 90665012.

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 21056609 - 2⁴ = 21056593 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21056689) 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, 1504037 + ... + 1504050.

It is an arithmetic number, because the mean of its divisors is an integer number (6016176).

Almost surely, 2^21056609 is an apocalyptic number.

It is an amenable number.

21056609 is a deficient number, since it is larger than the sum of its proper divisors (3008095).

21056609 is an equidigital number, since it uses as much as digits as its factorization.

21056609 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3008094.

The product of its (nonzero) digits is 3240, while the sum is 29.

The square root of 21056609 is about 4588.7480863521. The cubic root of 21056609 is about 276.1400998796.

The spelling of 21056609 in words is "twenty-one million, fifty-six thousand, six hundred nine".