21559609 has 4 divisors (see below), whose sum is σ = 21750516. Its totient is φ = 21368704.

The previous prime is 21559607. The next prime is 21559613. The reversal of 21559609 is 90695512.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 7683984 + 13875625 = 2772^2 + 3725^2 .

It is a cyclic number.

It is not a de Polignac number, because 21559609 - 2¹ = 21559607 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21559607) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 95284 + ... + 95509.

It is an arithmetic number, because the mean of its divisors is an integer number (5437629).

Almost surely, 2^21559609 is an apocalyptic number.

It is an amenable number.

21559609 is a deficient number, since it is larger than the sum of its proper divisors (190907).

21559609 is a wasteful number, since it uses less digits than its factorization.

21559609 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 190906.

The product of its (nonzero) digits is 24300, while the sum is 37.

The square root of 21559609 is about 4643.2326024010. The cubic root of 21559609 is about 278.3216305772.

The spelling of 21559609 in words is "twenty-one million, five hundred fifty-nine thousand, six hundred nine".