991871 has 2 divisors, whose sum is σ = 991872. Its totient is φ = 991870.

The previous prime is 991867. The next prime is 991873. The reversal of 991871 is 178199.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 991871 - 2² = 991867 is a prime.

It is a Sophie Germain prime.

Together with 991873, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (991873) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495935 + 495936.

It is an arithmetic number, because the mean of its divisors is an integer number (495936).

2⁹⁹¹⁸⁷¹ is an apocalyptic number.

991871 is a deficient number, since it is larger than the sum of its proper divisors (1).

991871 is an equidigital number, since it uses as much as digits as its factorization.

991871 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 4536, while the sum is 35.

The square root of 991871 is about 995.9272061752. The cubic root of 991871 is about 99.7282957701.

The spelling of 991871 in words is "nine hundred ninety-one thousand, eight hundred seventy-one".