991889 has 2 divisors, whose sum is σ = 991890. Its totient is φ = 991888.

The previous prime is 991883. The next prime is 991901. The reversal of 991889 is 988199.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 966289 + 25600 = 983^2 + 160^2 .

It is an emirp because it is prime and its reverse (988199) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 991889 - 2⁴ = 991873 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (991883) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495944 + 495945.

It is an arithmetic number, because the mean of its divisors is an integer number (495945).

2⁹⁹¹⁸⁸⁹ is an apocalyptic number.

It is an amenable number.

991889 is a deficient number, since it is larger than the sum of its proper divisors (1).

991889 is an equidigital number, since it uses as much as digits as its factorization.

991889 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 46656, while the sum is 44.

The square root of 991889 is about 995.9362429393. The cubic root of 991889 is about 99.7288990402.

The spelling of 991889 in words is "nine hundred ninety-one thousand, eight hundred eighty-nine".