20909 has 8 divisors (see below), whose sum is σ = 24960. Its totient is φ = 17136.

The previous prime is 20903. The next prime is 20921. The reversal of 20909 is 90902.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a de Polignac number, because none of the positive numbers 2^k-20909 is a prime.

It is a Duffinian number.

20909 is a modest number, since divided by 909 gives 2 as remainder.

It is a plaindrome in base 11.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20903) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 152 + ... + 254.

It is an arithmetic number, because the mean of its divisors is an integer number (3120).

2²⁰⁹⁰⁹ is an apocalyptic number.

20909 is a gapful number since it is divisible by the number (29) formed by its first and last digit.

It is an amenable number.

20909 is a deficient number, since it is larger than the sum of its proper divisors (4051).

20909 is a wasteful number, since it uses less digits than its factorization.

20909 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 139.

The product of its (nonzero) digits is 162, while the sum is 20.

The square root of 20909 is about 144.5994467486. The cubic root of 20909 is about 27.5493329351.

It can be divided in two parts, 20 and 909, that added together give a palindrome (929).

The spelling of 20909 in words is "twenty thousand, nine hundred nine".