19721138539 has 4 divisors (see below), whose sum is σ = 20202141960. Its totient is φ = 19240135120.

The previous prime is 19721138519. The next prime is 19721138551. The reversal of 19721138539 is 93583112791.

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-19721138539 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 19721138492 and 19721138501.

It is not an unprimeable number, because it can be changed into a prime (19721138519) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 240501649 + ... + 240501730.

It is an arithmetic number, because the mean of its divisors is an integer number (5050535490).

Almost surely, 2^19721138539 is an apocalyptic number.

19721138539 is a deficient number, since it is larger than the sum of its proper divisors (481003421).

19721138539 is an equidigital number, since it uses as much as digits as its factorization.

19721138539 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 481003420.

The product of its digits is 408240, while the sum is 49.

The spelling of 19721138539 in words is "nineteen billion, seven hundred twenty-one million, one hundred thirty-eight thousand, five hundred thirty-nine".