21805668 has 36 divisors (see below), whose sum is σ = 55635580. Its totient is φ = 7200576.

The previous prime is 21805661. The next prime is 21805669. The reversal of 21805668 is 86650812.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 18301284 + 3504384 = 4278^2 + 1872^2 .

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

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

It is not an unprimeable number, because it can be changed into a prime (21805661) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 1146 + ... + 6702.

Almost surely, 2^21805668 is an apocalyptic number.

It is an amenable number.

21805668 is an abundant number, since it is smaller than the sum of its proper divisors (33829912).

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

21805668 is a wasteful number, since it uses less digits than its factorization.

21805668 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5676 (or 5671 counting only the distinct ones).

The product of its (nonzero) digits is 23040, while the sum is 36.

The square root of 21805668 is about 4669.6539486347. The cubic root of 21805668 is about 279.3764525546.

The spelling of 21805668 in words is "twenty-one million, eight hundred five thousand, six hundred sixty-eight".