21664800 has 288 divisors, whose sum is σ = 84369600. Its totient is φ = 5345280.

The previous prime is 21664789. The next prime is 21664801. The reversal of 21664800 is 846612.

21664800 is a `hidden beast` number, since 2 + 16 + 648 + 0 + 0 = 666.

It is a tau number, because it is divible by the number of its divisors (288).

It is a Harshad number since it is a multiple of its sum of digits (27).

It is not an unprimeable number, because it can be changed into a prime (21664801) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 367171 + ... + 367229.

It is an arithmetic number, because the mean of its divisors is an integer number (292950).

Almost surely, 2^21664800 is an apocalyptic number.

21664800 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21664800, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (42184800).

21664800 is an abundant number, since it is smaller than the sum of its proper divisors (62704800).

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

21664800 is a wasteful number, since it uses less digits than its factorization.

21664800 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 105 (or 86 counting only the distinct ones).

The product of its (nonzero) digits is 2304, while the sum is 27.

The square root of 21664800 is about 4654.5461647727. The cubic root of 21664800 is about 278.7735473147.

The spelling of 21664800 in words is "twenty-one million, six hundred sixty-four thousand, eight hundred".