19989 has 6 divisors (see below), whose sum is σ = 28886. Its totient is φ = 13320.

The previous prime is 19979. The next prime is 19991. The reversal of 19989 is 98991.

It can be written as a sum of positive squares in only one way, i.e., 18225 + 1764 = 135^2 + 42^2 .

It is not a de Polignac number, because 19989 - 2⁴ = 19973 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (19919) 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 5 ways as a sum of consecutive naturals, for example, 1102 + ... + 1119.

2¹⁹⁹⁸⁹ is an apocalyptic number.

It is an amenable number.

19989 is a deficient number, since it is larger than the sum of its proper divisors (8897).

19989 is a wasteful number, since it uses less digits than its factorization.

19989 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2227 (or 2224 counting only the distinct ones).

The product of its digits is 5832, while the sum is 36.

The square root of 19989 is about 141.3824600154. The cubic root of 19989 is about 27.1391988210.

The spelling of 19989 in words is "nineteen thousand, nine hundred eighty-nine".