133991 has 8 divisors (see below), whose sum is σ = 157584. Its totient is φ = 112320.

The previous prime is 133981. The next prime is 133993. The reversal of 133991 is 199331.

133991 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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

It is not a de Polignac number, because 133991 - 2¹⁰ = 132967 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 133991.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (133993) 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, 326 + ... + 611.

It is an arithmetic number, because the mean of its divisors is an integer number (19698).

2¹³³⁹⁹¹ is an apocalyptic number.

133991 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

133991 is a deficient number, since it is larger than the sum of its proper divisors (23593).

133991 is a wasteful number, since it uses less digits than its factorization.

133991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 961.

The product of its digits is 729, while the sum is 26.

The square root of 133991 is about 366.0478110848. The cubic root of 133991 is about 51.1711537950.

It can be divided in two parts, 13 and 3991, that added together give a palindrome (4004).

The spelling of 133991 in words is "one hundred thirty-three thousand, nine hundred ninety-one".