21564644 has 12 divisors (see below), whose sum is σ = 37787904. Its totient is φ = 10768104.

The previous prime is 21564637. The next prime is 21564649. The reversal of 21564644 is 44646512.

It is a zygodrome in base 11.

It is a self number, because there is not a number n which added to its sum of digits gives 21564644.

It is not an unprimeable number, because it can be changed into a prime (21564649) 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, 329 + ... + 6575.

It is an arithmetic number, because the mean of its divisors is an integer number (3148992).

Almost surely, 2^21564644 is an apocalyptic number.

It is an amenable number.

21564644 is a deficient number, since it is larger than the sum of its proper divisors (16223260).

21564644 is a wasteful number, since it uses less digits than its factorization.

21564644 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7114 (or 7112 counting only the distinct ones).

The product of its digits is 23040, while the sum is 32.

The square root of 21564644 is about 4643.7747576729. The cubic root of 21564644 is about 278.3432951682.

The spelling of 21564644 in words is "twenty-one million, five hundred sixty-four thousand, six hundred forty-four".