1991777795905 has 4 divisors (see below), whose sum is σ = 2390133355092. Its totient is φ = 1593422236720.

The previous prime is 1991777795899. The next prime is 1991777795911. The reversal of 1991777795905 is 5095977771991.

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

It is an interprime number because it is at equal distance from previous prime (1991777795899) and next prime (1991777795911).

It can be written as a sum of positive squares in 2 ways, for example, as 462390480049 + 1529387315856 = 679993^2 + 1236684^2 .

It is not a de Polignac number, because 1991777795905 - 2²¹ = 1991775698753 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 199177779586 + ... + 199177779595.

It is an arithmetic number, because the mean of its divisors is an integer number (597533338773).

Almost surely, 2^{1991777795905} is an apocalyptic number.

It is an amenable number.

1991777795905 is a deficient number, since it is larger than the sum of its proper divisors (398355559187).

1991777795905 is an equidigital number, since it uses as much as digits as its factorization.

1991777795905 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 398355559186.

The product of its (nonzero) digits is 393824025, while the sum is 76.

The spelling of 1991777795905 in words is "one trillion, nine hundred ninety-one billion, seven hundred seventy-seven million, seven hundred ninety-five thousand, nine hundred five".