21288564 has 36 divisors (see below), whose sum is σ = 58705920. Its totient is φ = 6450960.

The previous prime is 21288559. The next prime is 21288571. The reversal of 21288564 is 46588212.

21288564 is a `hidden beast` number, since 2 + 12 + 88 + 564 = 666.

It is a tau number, because it is divible by the number of its divisors (36).

It is a hoax number, since the sum of its digits (36) coincides with the sum of the digits of its distinct prime factors.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 26484 + ... + 27275.

It is an arithmetic number, because the mean of its divisors is an integer number (1630720).

Almost surely, 2^21288564 is an apocalyptic number.

It is an amenable number.

21288564 is an abundant number, since it is smaller than the sum of its proper divisors (37417356).

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

21288564 is a wasteful number, since it uses less digits than its factorization.

21288564 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 53780 (or 53775 counting only the distinct ones).

The product of its digits is 30720, while the sum is 36.

The square root of 21288564 is about 4613.9531857183. The cubic root of 21288564 is about 277.1503656064.

The spelling of 21288564 in words is "twenty-one million, two hundred eighty-eight thousand, five hundred sixty-four".