19391660721 has 24 divisors (see below), whose sum is σ = 28329823080. Its totient is φ = 12780827136.

The previous prime is 19391660719. The next prime is 19391660747. The reversal of 19391660721 is 12706619391.

19391660721 is a `hidden beast` number, since 1 + 9 + 3 + 9 + 16 + 607 + 21 = 666.

It can be written as a sum of positive squares in 4 ways, for example, as 420455025 + 18971205696 = 20505^2 + 137736^2 .

It is not a de Polignac number, because 19391660721 - 2¹ = 19391660719 is a prime.

It is not an unprimeable number, because it can be changed into a prime (19391660711) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 379735 + ... + 427763.

It is an arithmetic number, because the mean of its divisors is an integer number (1180409295).

Almost surely, 2^19391660721 is an apocalyptic number.

It is an amenable number.

19391660721 is a deficient number, since it is larger than the sum of its proper divisors (8938162359).

19391660721 is a wasteful number, since it uses less digits than its factorization.

19391660721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 48545 (or 48542 counting only the distinct ones).

The product of its (nonzero) digits is 122472, while the sum is 45.

The spelling of 19391660721 in words is "nineteen billion, three hundred ninety-one million, six hundred sixty thousand, seven hundred twenty-one".