18971944639 has 4 divisors (see below), whose sum is σ = 18972510424. Its totient is φ = 18971378856.

The previous prime is 18971944627. The next prime is 18971944643. The reversal of 18971944639 is 93644917981.

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

It is a cyclic number.

It is not a de Polignac number, because 18971944639 - 2³³ = 10382010047 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 (18971944679) 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, 229197 + ... + 300790.

It is an arithmetic number, because the mean of its divisors is an integer number (4743127606).

Almost surely, 2^18971944639 is an apocalyptic number.

18971944639 is a deficient number, since it is larger than the sum of its proper divisors (565785).

18971944639 is an equidigital number, since it uses as much as digits as its factorization.

18971944639 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 565784.

The product of its digits is 11757312, while the sum is 61.

The spelling of 18971944639 in words is "eighteen billion, nine hundred seventy-one million, nine hundred forty-four thousand, six hundred thirty-nine".