16891812721 has 4 divisors (see below), whose sum is σ = 19304928832. Its totient is φ = 14478696612.

The previous prime is 16891812713. The next prime is 16891812727. The reversal of 16891812721 is 12721819861.

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: 12721819861 = 53 ⋅240034337.

It is a cyclic number.

It is not a de Polignac number, because 16891812721 - 2³ = 16891812713 is a prime.

It is not an unprimeable number, because it can be changed into a prime (16891812727) 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, 1206558045 + ... + 1206558058.

It is an arithmetic number, because the mean of its divisors is an integer number (4826232208).

Almost surely, 2^16891812721 is an apocalyptic number.

It is an amenable number.

16891812721 is a deficient number, since it is larger than the sum of its proper divisors (2413116111).

16891812721 is an equidigital number, since it uses as much as digits as its factorization.

16891812721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2413116110.

The product of its digits is 96768, while the sum is 46.

The spelling of 16891812721 in words is "sixteen billion, eight hundred ninety-one million, eight hundred twelve thousand, seven hundred twenty-one".