21855563 has 4 divisors (see below), whose sum is σ = 21938928. Its totient is φ = 21772200.

The previous prime is 21855553. The next prime is 21855571. The reversal of 21855563 is 36555812.

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

It is a cyclic number.

It is not a de Polignac number, because 21855563 - 2²⁴ = 5078347 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21855503) 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, 41288 + ... + 41813.

It is an arithmetic number, because the mean of its divisors is an integer number (5484732).

Almost surely, 2^21855563 is an apocalyptic number.

21855563 is a deficient number, since it is larger than the sum of its proper divisors (83365).

21855563 is an equidigital number, since it uses as much as digits as its factorization.

21855563 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 83364.

The product of its digits is 36000, while the sum is 35.

The square root of 21855563 is about 4674.9933689793. The cubic root of 21855563 is about 279.5893768524.

The spelling of 21855563 in words is "twenty-one million, eight hundred fifty-five thousand, five hundred sixty-three".