16691488721 has 4 divisors (see below), whose sum is σ = 17098598244. Its totient is φ = 16284379200.

The previous prime is 16691488687. The next prime is 16691488741. The reversal of 16691488721 is 12788419661.

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

It can be written as a sum of positive squares in 2 ways, for example, as 4567056400 + 12124432321 = 67580^2 + 110111^2 .

It is a cyclic number.

It is not a de Polignac number, because 16691488721 - 2²² = 16687294417 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (16691488741) 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, 203554700 + ... + 203554781.

It is an arithmetic number, because the mean of its divisors is an integer number (4274649561).

Almost surely, 2^16691488721 is an apocalyptic number.

It is an amenable number.

16691488721 is a deficient number, since it is larger than the sum of its proper divisors (407109523).

16691488721 is an equidigital number, since it uses as much as digits as its factorization.

16691488721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 407109522.

The product of its digits is 1161216, while the sum is 53.

The spelling of 16691488721 in words is "sixteen billion, six hundred ninety-one million, four hundred eighty-eight thousand, seven hundred twenty-one".