21864564 has 18 divisors (see below), whose sum is σ = 55268850. Its totient is φ = 7288176.

The previous prime is 21864553. The next prime is 21864569. The reversal of 21864564 is 46546812.

21864564 is a `hidden beast` number, since 2 + 1 + 8 + 645 + 6 + 4 = 666.

It can be written as a sum of positive squares in only one way, i.e., 21622500 + 242064 = 4650^2 + 492^2 .

It is a tau number, because it is divible by the number of its divisors (18).

It is a Harshad number since it is a multiple of its sum of digits (36), and also a Moran number because the ratio is a prime number: 607349 = 21864564 / (2 + 1 + 8 + 6 + 4 + 5 + 6 + 4).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21864569) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 303639 + ... + 303710.

Almost surely, 2^21864564 is an apocalyptic number.

It is an amenable number.

21864564 is an abundant number, since it is smaller than the sum of its proper divisors (33404286).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21864564 is a wasteful number, since it uses less digits than its factorization.

21864564 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 607359 (or 607354 counting only the distinct ones).

The product of its digits is 46080, while the sum is 36.

The square root of 21864564 is about 4675.9559450448. The cubic root of 21864564 is about 279.6277536352.

The spelling of 21864564 in words is "twenty-one million, eight hundred sixty-four thousand, five hundred sixty-four".