127991 has 4 divisors (see below), whose sum is σ = 129000. Its totient is φ = 126984.

The previous prime is 127979. The next prime is 127997. The reversal of 127991 is 199721.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 127991 - 2¹⁰ = 126967 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 (127997) 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, 281 + ... + 578.

It is an arithmetic number, because the mean of its divisors is an integer number (32250).

2¹²⁷⁹⁹¹ is an apocalyptic number.

127991 is a deficient number, since it is larger than the sum of its proper divisors (1009).

127991 is an equidigital number, since it uses as much as digits as its factorization.

127991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1008.

The product of its digits is 1134, while the sum is 29.

The square root of 127991 is about 357.7582982965. The cubic root of 127991 is about 50.3956607921.

The spelling of 127991 in words is "one hundred twenty-seven thousand, nine hundred ninety-one".