99998991 has 6 divisors (see below), whose sum is σ = 144443000. Its totient is φ = 66665988.

The previous prime is 99998971. The next prime is 99998999. The reversal of 99998991 is 19989999.

It is not a de Polignac number, because 99998991 - 2¹³ = 99990799 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 (99998999) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 5555491 + ... + 5555508.

Almost surely, 2^99998991 is an apocalyptic number.

99998991 is a deficient number, since it is larger than the sum of its proper divisors (44444009).

99998991 is a wasteful number, since it uses less digits than its factorization.

99998991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11111005 (or 11111002 counting only the distinct ones).

The product of its digits is 4251528, while the sum is 63.

The square root of 99998991 is about 9999.9495498727. The cubic root of 99998991 is about 464.1573222350.

The spelling of 99998991 in words is "ninety-nine million, nine hundred ninety-eight thousand, nine hundred ninety-one".