21563899 has 8 divisors (see below), whose sum is σ = 24922080. Its totient is φ = 18275136.

The previous prime is 21563897. The next prime is 21563923. The reversal of 21563899 is 99836512.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21563899 - 2¹ = 21563897 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21563891) 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 7 ways as a sum of consecutive naturals, for example, 16684 + ... + 17929.

It is an arithmetic number, because the mean of its divisors is an integer number (3115260).

Almost surely, 2^21563899 is an apocalyptic number.

21563899 is a deficient number, since it is larger than the sum of its proper divisors (3358181).

21563899 is an equidigital number, since it uses as much as digits as its factorization.

21563899 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 34709.

The product of its digits is 116640, while the sum is 43.

The square root of 21563899 is about 4643.6945420645. The cubic root of 21563899 is about 278.3400897958.

The spelling of 21563899 in words is "twenty-one million, five hundred sixty-three thousand, eight hundred ninety-nine".