33991 has 4 divisors (see below), whose sum is σ = 35800. Its totient is φ = 32184.

The previous prime is 33967. The next prime is 33997. The reversal of 33991 is 19933.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 19933 = 31 ⋅643.

It is a cyclic number.

It is not a de Polignac number, because 33991 - 2⁷ = 33863 is a prime.

It is a Duffinian number.

33991 is a lucky number.

It is a nialpdrome in base 15.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (33997) 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 3 ways as a sum of consecutive naturals, for example, 876 + ... + 913.

It is an arithmetic number, because the mean of its divisors is an integer number (8950).

2³³⁹⁹¹ is an apocalyptic number.

33991 is a deficient number, since it is larger than the sum of its proper divisors (1809).

33991 is a wasteful number, since it uses less digits than its factorization.

33991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1808.

The product of its digits is 729, while the sum is 25.

The square root of 33991 is about 184.3664828541. The cubic root of 33991 is about 32.3932592795.

It can be divided in two parts, 33 and 991, that added together give a 10-th power (1024 = 2¹⁰).

The spelling of 33991 in words is "thirty-three thousand, nine hundred ninety-one".