18991020823 has 4 divisors (see below), whose sum is σ = 19645883640. Its totient is φ = 18336158008.

The previous prime is 18991020817. The next prime is 18991020833. The reversal of 18991020823 is 32802019981.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-18991020823 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 18991020823.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18991020833) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 327431365 + ... + 327431422.

It is an arithmetic number, because the mean of its divisors is an integer number (4911470910).

Almost surely, 2^18991020823 is an apocalyptic number.

18991020823 is a deficient number, since it is larger than the sum of its proper divisors (654862817).

18991020823 is an equidigital number, since it uses as much as digits as its factorization.

18991020823 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 654862816.

The product of its (nonzero) digits is 62208, while the sum is 43.

The spelling of 18991020823 in words is "eighteen billion, nine hundred ninety-one million, twenty thousand, eight hundred twenty-three".