21805686 has 120 divisors (see below), whose sum is σ = 59093496. Its totient is φ = 5987520.

The previous prime is 21805681. The next prime is 21805699. The reversal of 21805686 is 68650812.

It is a happy number.

It is a self number, because there is not a number n which added to its sum of digits gives 21805686.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21805681) by changing a digit.

It is a polite number, since it can be written in 59 ways as a sum of consecutive naturals, for example, 325425 + ... + 325491.

Almost surely, 2^21805686 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21805686, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29546748).

21805686 is an abundant number, since it is smaller than the sum of its proper divisors (37287810).

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

21805686 is a wasteful number, since it uses less digits than its factorization.

21805686 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 136 (or 120 counting only the distinct ones).

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

The square root of 21805686 is about 4669.6558759720. The cubic root of 21805686 is about 279.3765294272.

The spelling of 21805686 in words is "twenty-one million, eight hundred five thousand, six hundred eighty-six".