16561999999 has 4 divisors (see below), whose sum is σ = 16563270064. Its totient is φ = 16560729936.

The previous prime is 16561999997. The next prime is 16562000033. The reversal of 16561999999 is 99999916561.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 99999916561 = 17 ⋅5882348033.

It is a cyclic number.

It is not a de Polignac number, because 16561999999 - 2¹ = 16561999997 is a prime.

It is a Duffinian number.

16561999999 is a modest number, since divided by 999999 gives 16561 as remainder.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (16561999997) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 615267 + ... + 641620.

It is an arithmetic number, because the mean of its divisors is an integer number (4140817516).

Almost surely, 2^16561999999 is an apocalyptic number.

16561999999 is a deficient number, since it is larger than the sum of its proper divisors (1270065).

16561999999 is a wasteful number, since it uses less digits than its factorization.

16561999999 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1270064.

The product of its digits is 95659380, while the sum is 73.

The spelling of 16561999999 in words is "sixteen billion, five hundred sixty-one million, nine hundred ninety-nine thousand, nine hundred ninety-nine".