21705685 has 8 divisors (see below), whose sum is σ = 27579096. Its totient is φ = 16343040.

The previous prime is 21705679. The next prime is 21705689. The reversal of 21705685 is 58650712.

It can be written as a sum of positive squares in 4 ways, for example, as 1572516 + 20133169 = 1254^2 + 4487^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21705685 - 2⁷ = 21705557 is a prime.

It is a super-2 number, since 2×21705685² = 942273522638450, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21705685.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21705689) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 127596 + ... + 127765.

It is an arithmetic number, because the mean of its divisors is an integer number (3447387).

Almost surely, 2^21705685 is an apocalyptic number.

It is an amenable number.

21705685 is a deficient number, since it is larger than the sum of its proper divisors (5873411).

21705685 is a wasteful number, since it uses less digits than its factorization.

21705685 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 255383.

The product of its (nonzero) digits is 16800, while the sum is 34.

The square root of 21705685 is about 4658.9360373373. The cubic root of 21705685 is about 278.9488007865.

The spelling of 21705685 in words is "twenty-one million, seven hundred five thousand, six hundred eighty-five".