989991 has 12 divisors (see below), whose sum is σ = 1438632. Its totient is φ = 656016.

The previous prime is 989981. The next prime is 989999. The reversal of 989991 is 199989.

989991 = 108² + 109² + ... + 161².

It is not a de Polignac number, because 989991 - 2⁵ = 989959 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (989999) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 2680 + ... + 3026.

It is an arithmetic number, because the mean of its divisors is an integer number (119886).

2⁹⁸⁹⁹⁹¹ is an apocalyptic number.

989991 is a deficient number, since it is larger than the sum of its proper divisors (448641).

989991 is a wasteful number, since it uses less digits than its factorization.

989991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 670 (or 667 counting only the distinct ones).

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

The square root of 989991 is about 994.9829144262. The cubic root of 989991 is about 99.6652473235.

It can be divided in two parts, 9 and 89991, that added together give a square (90000 = 300²).

The spelling of 989991 in words is "nine hundred eighty-nine thousand, nine hundred ninety-one".