1991082181991 has 8 divisors (see below), whose sum is σ = 2275861217280. Its totient is φ = 1706387827608.

The previous prime is 1991082181987. The next prime is 1991082182017. The reversal of 1991082181991 is 1991812801991.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 1991082181991 - 2² = 1991082181987 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 1991082181991.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1991082181961) 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, 21119831 + ... + 21213896.

It is an arithmetic number, because the mean of its divisors is an integer number (284482652160).

Almost surely, 2^{1991082181991} is an apocalyptic number.

1991082181991 is a deficient number, since it is larger than the sum of its proper divisors (284779035289).

1991082181991 is an equidigital number, since it uses as much as digits as its factorization.

1991082181991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 42340453.

The product of its (nonzero) digits is 839808, while the sum is 59.

The spelling of 1991082181991 in words is "one trillion, nine hundred ninety-one billion, eighty-two million, one hundred eighty-one thousand, nine hundred ninety-one".