21686805 has 64 divisors (see below), whose sum is σ = 44997120. Its totient is φ = 9704448.

The previous prime is 21686741. The next prime is 21686813. The reversal of 21686805 is 50868612.

It is a happy number.

It is not a de Polignac number, because 21686805 - 2⁶ = 21686741 is a prime.

It is a super-2 number, since 2×21686805² = 940635022216050, which contains 22 as substring.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21686805.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 49869 + ... + 50301.

It is an arithmetic number, because the mean of its divisors is an integer number (703080).

Almost surely, 2^21686805 is an apocalyptic number.

It is an amenable number.

21686805 is an abundant number, since it is smaller than the sum of its proper divisors (23310315).

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

21686805 is a wasteful number, since it uses less digits than its factorization.

21686805 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 507 (or 501 counting only the distinct ones).

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

The square root of 21686805 is about 4656.9093828418. The cubic root of 21686805 is about 278.8678990768.

The spelling of 21686805 in words is "twenty-one million, six hundred eighty-six thousand, eight hundred five".