16561345909 has 2 divisors, whose sum is σ = 16561345910. Its totient is φ = 16561345908.

The previous prime is 16561345907. The next prime is 16561345921. The reversal of 16561345909 is 90954316561.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 16058465284 + 502880625 = 126722^2 + 22425^2 .

It is an emirp because it is prime and its reverse (90954316561) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 16561345909 - 2¹ = 16561345907 is a prime.

Together with 16561345907, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (16561345907) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 8280672954 + 8280672955.

It is an arithmetic number, because the mean of its divisors is an integer number (8280672955).

Almost surely, 2^16561345909 is an apocalyptic number.

It is an amenable number.

16561345909 is a deficient number, since it is larger than the sum of its proper divisors (1).

16561345909 is an equidigital number, since it uses as much as digits as its factorization.

16561345909 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 874800, while the sum is 49.

The spelling of 16561345909 in words is "sixteen billion, five hundred sixty-one million, three hundred forty-five thousand, nine hundred nine".