42991 has 4 divisors (see below), whose sum is σ = 46312. Its totient is φ = 39672.

The previous prime is 42989. The next prime is 43003. The reversal of 42991 is 19924.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 42991 - 2¹ = 42989 is a prime.

It is an Ulam number.

It is a Duffinian 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 (42901) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1641 + ... + 1666.

It is an arithmetic number, because the mean of its divisors is an integer number (11578).

2⁴²⁹⁹¹ is an apocalyptic number.

42991 is a deficient number, since it is larger than the sum of its proper divisors (3321).

42991 is a wasteful number, since it uses less digits than its factorization.

42991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3320.

The product of its digits is 648, while the sum is 25.

The square root of 42991 is about 207.3427114706. The cubic root of 42991 is about 35.0315362021.

The spelling of 42991 in words is "forty-two thousand, nine hundred ninety-one".