20709 has 16 divisors (see below), whose sum is σ = 33600. Its totient is φ = 12528.

The previous prime is 20707. The next prime is 20717. The reversal of 20709 is 90702.

It is not a de Polignac number, because 20709 - 2¹ = 20707 is a prime.

It is an Ulam number.

It is a nialpdrome in base 12.

It is a zygodrome in base 12.

It is a junction number, because it is equal to n+sod(n) for n = 20691 and 20700.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20707) 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, 322 + ... + 380.

It is an arithmetic number, because the mean of its divisors is an integer number (2100).

2²⁰⁷⁰⁹ is an apocalyptic number.

It is an amenable number.

20709 is a deficient number, since it is larger than the sum of its proper divisors (12891).

20709 is a wasteful number, since it uses less digits than its factorization.

20709 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 81 (or 75 counting only the distinct ones).

The product of its (nonzero) digits is 126, while the sum is 18.

The square root of 20709 is about 143.9062194625. The cubic root of 20709 is about 27.4612125354.

It can be divided in two parts, 20 and 709, that added together give a 6-th power (729 = 3⁶).

The spelling of 20709 in words is "twenty thousand, seven hundred nine".