999989991 has 144 divisors (see below), whose sum is σ = 2006248608. Its totient is φ = 471744000.

The previous prime is 999989981. The next prime is 999990011. The reversal of 999989991 is 199989999.

It is a happy number.

It is not a de Polignac number, because 999989991 - 2⁷ = 999989863 is a prime.

999989991 is a modest number, since divided by 89991 gives 9999 as remainder.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (999989981) by changing a digit.

It is a polite number, since it can be written in 143 ways as a sum of consecutive naturals, for example, 6369285 + ... + 6369441.

It is an arithmetic number, because the mean of its divisors is an integer number (13932282).

Almost surely, 2^999989991 is an apocalyptic number.

999989991 is a gapful number since it is divisible by the number (91) formed by its first and last digit.

999989991 is a primitive abundant number, since it is smaller than the sum of its proper divisors, none of which is abundant.

999989991 is a wasteful number, since it uses less digits than its factorization.

999989991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 302 (or 292 counting only the distinct ones).

The product of its digits is 38263752, while the sum is 72.

The square root of 999989991 is about 31622.6183451023. The cubic root of 999989991 is about 999.9966636555.

It can be divided in two parts, 999989 and 991, that multiplied together give a palindrome (990989099).

The spelling of 999989991 in words is "nine hundred ninety-nine million, nine hundred eighty-nine thousand, nine hundred ninety-one".