39991 has 8 divisors (see below), whose sum is σ = 47520. Its totient is φ = 32928.

The previous prime is 39989. The next prime is 40009. The reversal of 39991 is 19993.

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

It is not a de Polignac number, because 39991 - 2¹ = 39989 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 (39901) 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, 105 + ... + 301.

It is an arithmetic number, because the mean of its divisors is an integer number (5940).

2³⁹⁹⁹¹ is an apocalyptic number.

39991 is a deficient number, since it is larger than the sum of its proper divisors (7529).

39991 is a wasteful number, since it uses less digits than its factorization.

39991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 233.

The product of its digits is 2187, while the sum is 31.

The square root of 39991 is about 199.9774987342. The cubic root of 39991 is about 34.1969537772.

The spelling of 39991 in words is "thirty-nine thousand, nine hundred ninety-one".