21664368 has 160 divisors (see below), whose sum is σ = 69995520. Its totient is φ = 6359040.

The previous prime is 21664361. The next prime is 21664373. The reversal of 21664368 is 86346612.

21664368 is a `hidden beast` number, since 2 + 1 + 6 + 643 + 6 + 8 = 666.

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

It is a nude number because it is divisible by every one of its digits.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21664361) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 223296 + ... + 223392.

It is an arithmetic number, because the mean of its divisors is an integer number (437472).

Almost surely, 2^21664368 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21664368, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (34997760).

21664368 is an abundant number, since it is smaller than the sum of its proper divisors (48331152).

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

21664368 is a wasteful number, since it uses less digits than its factorization.

21664368 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 172 (or 160 counting only the distinct ones).

The product of its digits is 41472, while the sum is 36.

The square root of 21664368 is about 4654.4997582984. The cubic root of 21664368 is about 278.7716943708.

The spelling of 21664368 in words is "twenty-one million, six hundred sixty-four thousand, three hundred sixty-eight".