21685135 has 4 divisors (see below), whose sum is σ = 26022168. Its totient is φ = 17348104.

The previous prime is 21685133. The next prime is 21685163. The reversal of 21685135 is 53158612.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21685135 - 2¹ = 21685133 is a prime.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21685097 and 21685106.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21685133) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2168509 + ... + 2168518.

It is an arithmetic number, because the mean of its divisors is an integer number (6505542).

Almost surely, 2^21685135 is an apocalyptic number.

21685135 is a deficient number, since it is larger than the sum of its proper divisors (4337033).

21685135 is an equidigital number, since it uses as much as digits as its factorization.

21685135 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4337032.

The product of its digits is 7200, while the sum is 31.

The square root of 21685135 is about 4656.7300759224. The cubic root of 21685135 is about 278.8607407864.

The spelling of 21685135 in words is "twenty-one million, six hundred eighty-five thousand, one hundred thirty-five".