21685685 has 12 divisors (see below), whose sum is σ = 30271788. Its totient is φ = 14870016.

The previous prime is 21685667. The next prime is 21685687. The reversal of 21685685 is 58658612.

It can be written as a sum of positive squares in 2 ways, for example, as 13608721 + 8076964 = 3689^2 + 2842^2 .

It is not a de Polignac number, because 21685685 - 2⁶ = 21685621 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21685687) 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, 44012 + ... + 44501.

It is an arithmetic number, because the mean of its divisors is an integer number (2522649).

Almost surely, 2^21685685 is an apocalyptic number.

It is an amenable number.

21685685 is a deficient number, since it is larger than the sum of its proper divisors (8586103).

21685685 is an equidigital number, since it uses as much as digits as its factorization.

21685685 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 88532 (or 88525 counting only the distinct ones).

The product of its digits is 115200, while the sum is 41.

The square root of 21685685 is about 4656.7891298619. The cubic root of 21685685 is about 278.8630983477.

The spelling of 21685685 in words is "twenty-one million, six hundred eighty-five thousand, six hundred eighty-five".