99999000991 has 4 divisors (see below), whose sum is σ = 99999685584. Its totient is φ = 99998316400.

The previous prime is 99999000979. The next prime is 99999001007. The reversal of 99999000991 is 19900099999.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-99999000991 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (99999000901) 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, 25390 + ... + 447931.

It is an arithmetic number, because the mean of its divisors is an integer number (24999921396).

Almost surely, 2^99999000991 is an apocalyptic number.

99999000991 is a deficient number, since it is larger than the sum of its proper divisors (684593).

99999000991 is a wasteful number, since it uses less digits than its factorization.

99999000991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 684592.

The product of its (nonzero) digits is 4782969, while the sum is 64.

The spelling of 99999000991 in words is "ninety-nine billion, nine hundred ninety-nine million, nine hundred ninety-one", and thus it is an aban number.