99959981991 has 4 divisors (see below), whose sum is σ = 133279975992. Its totient is φ = 66639987992.

The previous prime is 99959981971. The next prime is 99959982013. The reversal of 99959981991 is 19918995999.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 99959981991 - 2¹⁴ = 99959965607 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (99959981971) 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, 16659996996 + ... + 16659997001.

It is an arithmetic number, because the mean of its divisors is an integer number (33319993998).

Almost surely, 2^99959981991 is an apocalyptic number.

99959981991 is a deficient number, since it is larger than the sum of its proper divisors (33319994001).

99959981991 is a wasteful number, since it uses less digits than its factorization.

99959981991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 33319994000.

The product of its digits is 191318760, while the sum is 78.

The spelling of 99959981991 in words is "ninety-nine billion, nine hundred fifty-nine million, nine hundred eighty-one thousand, nine hundred ninety-one".