20559 has 16 divisors (see below), whose sum is σ = 34560. Its totient is φ = 10560.

The previous prime is 20551. The next prime is 20563. The reversal of 20559 is 95502.

It is not a de Polignac number, because 20559 - 2³ = 20551 is a prime.

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

It is a nialpdrome in base 12.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20551) 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, 187 + ... + 275.

It is an arithmetic number, because the mean of its divisors is an integer number (2160).

2²⁰⁵⁵⁹ is an apocalyptic number.

20559 is the 77-th nonagonal number.

20559 is a deficient number, since it is larger than the sum of its proper divisors (14001).

20559 is a wasteful number, since it uses less digits than its factorization.

20559 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 110.

The product of its (nonzero) digits is 450, while the sum is 21.

The square root of 20559 is about 143.3840995369. The cubic root of 20559 is about 27.3947492025.

20559 divided by its sum of digits (21) gives a palindrome (979).

The spelling of 20559 in words is "twenty thousand, five hundred fifty-nine".