20989 has 4 divisors (see below), whose sum is σ = 21280. Its totient is φ = 20700.

The previous prime is 20983. The next prime is 21001. The reversal of 20989 is 98902.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 98902 = 2 ⋅49451.

It is a cyclic number.

It is not a de Polignac number, because 20989 - 2³ = 20981 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20981) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 64 + ... + 214.

It is an arithmetic number, because the mean of its divisors is an integer number (5320).

2²⁰⁹⁸⁹ is an apocalyptic number.

It is an amenable number.

20989 is a deficient number, since it is larger than the sum of its proper divisors (291).

20989 is a wasteful number, since it uses less digits than its factorization.

20989 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 290.

The product of its (nonzero) digits is 1296, while the sum is 28.

The square root of 20989 is about 144.8758088847. The cubic root of 20989 is about 27.5844237533.

The spelling of 20989 in words is "twenty thousand, nine hundred eighty-nine".