20659 has 4 divisors (see below), whose sum is σ = 21016. Its totient is φ = 20304.

The previous prime is 20641. The next prime is 20663. The reversal of 20659 is 95602.

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 20659 - 2⁵ = 20627 is a prime.

It is a Duffinian number.

It is a nialpdrome in base 13.

It is not an unprimeable number, because it can be changed into a prime (20639) 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 3 ways as a sum of consecutive naturals, for example, 69 + ... + 214.

It is an arithmetic number, because the mean of its divisors is an integer number (5254).

2²⁰⁶⁵⁹ is an apocalyptic number.

20659 is a deficient number, since it is larger than the sum of its proper divisors (357).

20659 is an equidigital number, since it uses as much as digits as its factorization.

20659 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 356.

The product of its (nonzero) digits is 540, while the sum is 22.

The square root of 20659 is about 143.7323902257. The cubic root of 20659 is about 27.4390938567.

The spelling of 20659 in words is "twenty thousand, six hundred fifty-nine".