20685 has 16 divisors (see below), whose sum is σ = 38016. Its totient is φ = 9408.

The previous prime is 20681. The next prime is 20693. The reversal of 20685 is 58602.

20685 = 25² + 26² + ... + 42².

It is a happy number.

20685 is nontrivially palindromic in base 14.

It is not a de Polignac number, because 20685 - 2² = 20681 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (21).

20685 is a nontrivial repdigit in base 14.

It is a plaindrome in base 14.

It is a nialpdrome in base 13 and base 14.

It is a zygodrome in base 14.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20681) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 7 + ... + 203.

It is an arithmetic number, because the mean of its divisors is an integer number (2376).

2²⁰⁶⁸⁵ is an apocalyptic number.

It is an amenable number.

20685 is a deficient number, since it is larger than the sum of its proper divisors (17331).

20685 is a wasteful number, since it uses less digits than its factorization.

20685 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 212.

The product of its (nonzero) digits is 480, while the sum is 21.

The square root of 20685 is about 143.8228076489. The cubic root of 20685 is about 27.4506000181.

Adding to 20685 its sum of digits (21), we get a triangular number (20706 = T₂₀₃).

The spelling of 20685 in words is "twenty thousand, six hundred eighty-five".