243991 has 8 divisors (see below), whose sum is σ = 273168. Its totient is φ = 216000.

The previous prime is 243989. The next prime is 244003. The reversal of 243991 is 199342.

243991 = 10³ + 11³ + ... + 31³.

It is a happy number.

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

It is a 6-Lehmer number, since φ(243991) divides (243991-1)⁶.

It is a cyclic number.

It is not a de Polignac number, because 243991 - 2¹ = 243989 is a prime.

It is an Ulam number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (243911) 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 7 ways as a sum of consecutive naturals, for example, 181 + ... + 721.

It is an arithmetic number, because the mean of its divisors is an integer number (34146).

2²⁴³⁹⁹¹ is an apocalyptic number.

243991 is a deficient number, since it is larger than the sum of its proper divisors (29177).

243991 is a wasteful number, since it uses less digits than its factorization.

243991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 593.

The product of its digits is 1944, while the sum is 28.

The square root of 243991 is about 493.9544513414. The cubic root of 243991 is about 62.4872293908.

The spelling of 243991 in words is "two hundred forty-three thousand, nine hundred ninety-one".