991959 has 4 divisors (see below), whose sum is σ = 1322616. Its totient is φ = 661304.

The previous prime is 991957. The next prime is 991961. The reversal of 991959 is 959199.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 959199 = 3 ⋅319733.

It is an interprime number because it is at equal distance from previous prime (991957) and next prime (991961).

It is a cyclic number.

It is not a de Polignac number, because 991959 - 2¹ = 991957 is a prime.

It is a D-number.

It is a self number, because there is not a number n which added to its sum of digits gives 991959.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 991959.

It is not an unprimeable number, because it can be changed into a prime (991951) 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, 165324 + ... + 165329.

It is an arithmetic number, because the mean of its divisors is an integer number (330654).

2⁹⁹¹⁹⁵⁹ is an apocalyptic number.

991959 is a deficient number, since it is larger than the sum of its proper divisors (330657).

991959 is a wasteful number, since it uses less digits than its factorization.

991959 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 330656.

The product of its digits is 32805, while the sum is 42.

The square root of 991959 is about 995.9713851311. The cubic root of 991959 is about 99.7312450213.

The spelling of 991959 in words is "nine hundred ninety-one thousand, nine hundred fifty-nine".