21564378 has 36 divisors (see below), whose sum is σ = 51361674. Its totient is φ = 6534000.

The previous prime is 21564353. The next prime is 21564379. The reversal of 21564378 is 87346512.

21564378 is a `hidden beast` number, since 2 + 1 + 5 + 643 + 7 + 8 = 666.

It can be written as a sum of positive squares in only one way, i.e., 12938409 + 8625969 = 3597^2 + 2937^2 .

It is not an unprimeable number, because it can be changed into a prime (21564379) by changing a digit.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 2773 + ... + 7128.

Almost surely, 2^21564378 is an apocalyptic number.

21564378 is an abundant number, since it is smaller than the sum of its proper divisors (29797296).

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

21564378 is a wasteful number, since it uses less digits than its factorization.

21564378 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9931 (or 9917 counting only the distinct ones).

The product of its digits is 40320, while the sum is 36.

The square root of 21564378 is about 4643.7461170912. The cubic root of 21564378 is about 278.3421507081.

The spelling of 21564378 in words is "twenty-one million, five hundred sixty-four thousand, three hundred seventy-eight".