991991891990 has 16 divisors (see below), whose sum is σ = 1947911351760. Its totient is φ = 360724324320.

The previous prime is 991991891977. The next prime is 991991891999. The reversal of 991991891990 is 99198199199.

991991891990 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (991991891999) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 4509053945 + ... + 4509054164.

It is an arithmetic number, because the mean of its divisors is an integer number (121744459485).

Almost surely, 2^991991891990 is an apocalyptic number.

991991891990 is a deficient number, since it is larger than the sum of its proper divisors (955919459770).

991991891990 is a wasteful number, since it uses less digits than its factorization.

991991891990 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9018108127.

The product of its (nonzero) digits is 38263752, while the sum is 74.

The spelling of 991991891990 in words is "nine hundred ninety-one billion, nine hundred ninety-one million, eight hundred ninety-one thousand, nine hundred ninety".