18991644338 has 4 divisors (see below), whose sum is σ = 28487466510. Its totient is φ = 9495822168.

The previous prime is 18991644311. The next prime is 18991644349. The reversal of 18991644338 is 83344619981.

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

It can be written as a sum of positive squares in only one way, i.e., 17032077049 + 1959567289 = 130507^2 + 44267^2 .

It is a super-2 number, since 2×18991644338² (a number of 21 digits) contains 22 as substring.

It is a Curzon number.

It is an unprimeable number.

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 as a sum of consecutive naturals, namely, 4747911083 + ... + 4747911086.

Almost surely, 2^18991644338 is an apocalyptic number.

18991644338 is a deficient number, since it is larger than the sum of its proper divisors (9495822172).

18991644338 is an equidigital number, since it uses as much as digits as its factorization.

18991644338 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9495822171.

The product of its digits is 4478976, while the sum is 56.

The spelling of 18991644338 in words is "eighteen billion, nine hundred ninety-one million, six hundred forty-four thousand, three hundred thirty-eight".