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31989 = 310663

31989 has 4 divisors (see below), whose sum is σ = 42656. Its totient is φ = 21324.

The previous prime is 31981. The next prime is 31991. The reversal of 31989 is 98913.

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 an emirpimes, since its reverse is a distinct semiprime: 98913 = 332971.

It is not a de Polignac number, because 31989 - 23 = 31981 is a prime.

It is a super-2 number, since 2×319892 = 2046592242, which contains 22 as substring.

It is a D-number.

It is a Duffinian number.

31989 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (31981) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 5329 + ... + 5334.

It is an arithmetic number, because the mean of its divisors is an integer number (10664).

231989 is an apocalyptic number.

It is an amenable number.

31989 is a deficient number, since it is larger than the sum of its proper divisors (10667).

31989 is a wasteful number, since it uses less digits than its factorization.

31989 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10666.

The product of its digits is 1944, while the sum is 30.

The square root of 31989 is about 178.8546896226. The cubic root of 31989 is about 31.7443828284.

Adding to 31989 its product of digits (1944), we get a palindrome (33933).

It can be divided in two parts, 3198 and 9, that multiplied together give a palindrome (28782).

The spelling of 31989 in words is "thirty-one thousand, nine hundred eighty-nine".

Divisors: 1 3 10663 31989