1991173965191 has 16 divisors (see below), whose sum is σ = 2024645436000. Its totient is φ = 1958042486400.

The previous prime is 1991173965149. The next prime is 1991173965217. The reversal of 1991173965191 is 1915693711991.

It is a cyclic number.

It is not a de Polignac number, because 1991173965191 - 2³⁸ = 1716296058247 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 (1991173965091) 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, 8096345 + ... + 8338653.

It is an arithmetic number, because the mean of its divisors is an integer number (126540339750).

Almost surely, 2^{1991173965191} is an apocalyptic number.

1991173965191 is a deficient number, since it is larger than the sum of its proper divisors (33471470809).

1991173965191 is a wasteful number, since it uses less digits than its factorization.

1991173965191 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 243010.

The product of its digits is 4133430, while the sum is 62.

The spelling of 1991173965191 in words is "one trillion, nine hundred ninety-one billion, one hundred seventy-three million, nine hundred sixty-five thousand, one hundred ninety-one".