998991 has 24 divisors (see below), whose sum is σ = 1676064. Its totient is φ = 561600.

The previous prime is 998989. The next prime is 999007. The reversal of 998991 is 199899.

998991 is a nontrivial binomial coefficient, being equal to C(1414, 2).

It is not a de Polignac number, because 998991 - 2¹ = 998989 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (998941) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 6285 + ... + 6441.

It is an arithmetic number, because the mean of its divisors is an integer number (69836).

2⁹⁹⁸⁹⁹¹ is an apocalyptic number.

998991 is the 1413-rd triangular number and also the 707-th hexagonal number.

998991 is a deficient number, since it is larger than the sum of its proper divisors (677073).

998991 is a wasteful number, since it uses less digits than its factorization.

998991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 271 (or 268 counting only the distinct ones).

The product of its digits is 52488, while the sum is 45.

The square root of 998991 is about 999.4953726756. The cubic root of 998991 is about 99.9663553483.

The spelling of 998991 in words is "nine hundred ninety-eight thousand, nine hundred ninety-one".