16991434561 has 4 divisors (see below), whose sum is σ = 16996977712. Its totient is φ = 16985891412.

The previous prime is 16991434547. The next prime is 16991434633. The reversal of 16991434561 is 16543419961.

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: 16543419961 = 88003 ⋅187987.

It is a cyclic number.

It is not a de Polignac number, because 16991434561 - 2¹⁹ = 16990910273 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (16991434541) 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, 2766975 + ... + 2773108.

It is an arithmetic number, because the mean of its divisors is an integer number (4249244428).

Almost surely, 2^16991434561 is an apocalyptic number.

It is an amenable number.

16991434561 is a deficient number, since it is larger than the sum of its proper divisors (5543151).

16991434561 is an equidigital number, since it uses as much as digits as its factorization.

16991434561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5543150.

The product of its digits is 699840, while the sum is 49.

The spelling of 16991434561 in words is "sixteen billion, nine hundred ninety-one million, four hundred thirty-four thousand, five hundred sixty-one".