8999999991 has 28 divisors (see below), whose sum is σ = 13858566712. Its totient is φ = 5837820336.

The previous prime is 8999999929. The next prime is 8999999993. The reversal of 8999999991 is 1999999998.

8999999991 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is not a de Polignac number, because 8999999991 - 2⁹ = 8999999479 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (81).

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 8999999991.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (8999999993) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 27 ways as a sum of consecutive naturals, for example, 139861 + ... + 193806.

Almost surely, 2^8999999991 is an apocalyptic number.

8999999991 is a gapful number since it is divisible by the number (81) formed by its first and last digit.

8999999991 is a deficient number, since it is larger than the sum of its proper divisors (4858566721).

8999999991 is an equidigital number, since it uses as much as digits as its factorization.

8999999991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 333722 (or 333707 counting only the distinct ones).

The product of its digits is 344373768, while the sum is 81.

The square root of 8999999991 is about 94868.3297576172. The cubic root of 8999999991 is about 2080.0838223585.

8999999991 divided by its sum of digits (81) gives a palindrome (111111111).

It can be divided in two parts, 899999999 and 1, that added together give a square (900000000 = 30000²).

The spelling of 8999999991 in words is "eight billion, nine hundred ninety-nine million, nine hundred ninety-nine thousand, nine hundred ninety-one".