18391970991 has 4 divisors (see below), whose sum is σ = 24522627992. Its totient is φ = 12261313992.

The previous prime is 18391970923. The next prime is 18391971001. The reversal of 18391970991 is 19907919381.

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

It is not a de Polignac number, because 18391970991 - 2¹⁸ = 18391708847 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 (18391980991) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3065328496 + ... + 3065328501.

It is an arithmetic number, because the mean of its divisors is an integer number (6130656998).

Almost surely, 2^18391970991 is an apocalyptic number.

18391970991 is a deficient number, since it is larger than the sum of its proper divisors (6130657001).

18391970991 is an equidigital number, since it uses as much as digits as its factorization.

18391970991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6130657000.

The product of its (nonzero) digits is 1102248, while the sum is 57.

The spelling of 18391970991 in words is "eighteen billion, three hundred ninety-one million, nine hundred seventy thousand, nine hundred ninety-one".