18728478721 has 8 divisors (see below), whose sum is σ = 18815888520. Its totient is φ = 18641129472.

The previous prime is 18728478707. The next prime is 18728478751. The reversal of 18728478721 is 12787482781.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 269452225 + 18459026496 = 16415^2 + 135864^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-18728478721 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (18728478751) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 678241 + ... + 705313.

It is an arithmetic number, because the mean of its divisors is an integer number (2351986065).

Almost surely, 2^18728478721 is an apocalyptic number.

It is an amenable number.

18728478721 is a deficient number, since it is larger than the sum of its proper divisors (87409799).

18728478721 is a wasteful number, since it uses less digits than its factorization.

18728478721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 30275.

The product of its digits is 2809856, while the sum is 55.

The spelling of 18728478721 in words is "eighteen billion, seven hundred twenty-eight million, four hundred seventy-eight thousand, seven hundred twenty-one".