991991100051 has 16 divisors (see below), whose sum is σ = 1679561651200. Its totient is φ = 566852057064.

The previous prime is 991991100011. The next prime is 991991100109. The reversal of 991991100051 is 150001199199.

It is not a de Polignac number, because 991991100051 - 2⁷ = 991991099923 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (991991100011) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 2624314891 + ... + 2624315268.

It is an arithmetic number, because the mean of its divisors is an integer number (104972603200).

Almost surely, 2^991991100051 is an apocalyptic number.

991991100051 is a deficient number, since it is larger than the sum of its proper divisors (687570551149).

991991100051 is a wasteful number, since it uses less digits than its factorization.

991991100051 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5248630175 (or 5248630169 counting only the distinct ones).

The product of its (nonzero) digits is 32805, while the sum is 45.

The spelling of 991991100051 in words is "nine hundred ninety-one billion, nine hundred ninety-one million, one hundred thousand, fifty-one".