21621888 has 72 divisors (see below), whose sum is σ = 62676705. Its totient is φ = 7154688.

The previous prime is 21621881. The next prime is 21621923. The reversal of 21621888 is 88812612.

It is a powerful number, because all its prime factors have an exponent greater than 1 and also an Achilles number because it is not a perfect power.

21621888 is a `hidden beast` number, since 21 + 621 + 8 + 8 + 8 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 21455424 + 166464 = 4632^2 + 408^2 .

It is a tau number, because it is divible by the number of its divisors (72).

It is an ABA number since it can be written as A⋅B^A, here for A=2, B=3288.

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 not an unprimeable number, because it can be changed into a prime (21621881) by changing a digit.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 157756 + ... + 157892.

Almost surely, 2^21621888 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 21621888

21621888 is an abundant number, since it is smaller than the sum of its proper divisors (41054817).

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

21621888 is an equidigital number, since it uses as much as digits as its factorization.

21621888 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 294 (or 142 counting only the distinct ones).

The product of its digits is 12288, while the sum is 36.

The square root of 21621888 is about 4649.9341930827. The cubic root of 21621888 is about 278.5893677937.

The spelling of 21621888 in words is "twenty-one million, six hundred twenty-one thousand, eight hundred eighty-eight".