991900990991 has 16 divisors (see below), whose sum is σ = 1034158748928. Its totient is φ = 950286816000.

The previous prime is 991900990987. The next prime is 991900991009. The reversal of 991900990991 is 199099009199.

It is a cyclic number.

It is not a de Polignac number, because 991900990991 - 2² = 991900990987 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 (991900990931) 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, 39290825 + ... + 39316061.

It is an arithmetic number, because the mean of its divisors is an integer number (64634921808).

Almost surely, 2^991900990991 is an apocalyptic number.

991900990991 is a deficient number, since it is larger than the sum of its proper divisors (42257757937).

991900990991 is a wasteful number, since it uses less digits than its factorization.

991900990991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 37922.

The product of its (nonzero) digits is 4782969, while the sum is 65.

It can be divided in two parts, 991900 and 990991, that added together give a palindrome (1982891).

The spelling of 991900990991 in words is "nine hundred ninety-one billion, nine hundred million, nine hundred ninety thousand, nine hundred ninety-one".