21559809 has 16 divisors (see below), whose sum is σ = 30731904. Its totient is φ = 13411200.

The previous prime is 21559801. The next prime is 21559829. The reversal of 21559809 is 90895512.

It is not a de Polignac number, because 21559809 - 2³ = 21559801 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21559801) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 982 + ... + 6639.

It is an arithmetic number, because the mean of its divisors is an integer number (1920744).

Almost surely, 2^21559809 is an apocalyptic number.

It is an amenable number.

21559809 is a deficient number, since it is larger than the sum of its proper divisors (9172095).

21559809 is a wasteful number, since it uses less digits than its factorization.

21559809 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7688.

The product of its (nonzero) digits is 32400, while the sum is 39.

The square root of 21559809 is about 4643.2541390710. The cubic root of 21559809 is about 278.3224912012.

The spelling of 21559809 in words is "twenty-one million, five hundred fifty-nine thousand, eight hundred nine".