18156038721 has 4 divisors (see below), whose sum is σ = 24208051632. Its totient is φ = 12104025812.

The previous prime is 18156038689. The next prime is 18156038723. The reversal of 18156038721 is 12783065181.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 12783065181 = 3 ⋅4261021727.

It is a cyclic number.

It is not a de Polignac number, because 18156038721 - 2⁵ = 18156038689 is a prime.

It is not an unprimeable number, because it can be changed into a prime (18156038723) 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, 3026006451 + ... + 3026006456.

It is an arithmetic number, because the mean of its divisors is an integer number (6052012908).

Almost surely, 2^18156038721 is an apocalyptic number.

It is an amenable number.

18156038721 is a deficient number, since it is larger than the sum of its proper divisors (6052012911).

18156038721 is an equidigital number, since it uses as much as digits as its factorization.

18156038721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6052012910.

The product of its (nonzero) digits is 80640, while the sum is 42.

The spelling of 18156038721 in words is "eighteen billion, one hundred fifty-six million, thirty-eight thousand, seven hundred twenty-one".