2809856561 has 4 divisors (see below), whose sum is σ = 2810374512. Its totient is φ = 2809338612.

The previous prime is 2809856557. The next prime is 2809856563. The reversal of 2809856561 is 1656589082.

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.

It is a cyclic number.

It is not a de Polignac number, because 2809856561 - 2² = 2809856557 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (2809856563) 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, 250751 + ... + 261716.

It is an arithmetic number, because the mean of its divisors is an integer number (702593628).

Almost surely, 2^2809856561 is an apocalyptic number.

It is an amenable number.

2809856561 is a deficient number, since it is larger than the sum of its proper divisors (517951).

2809856561 is an equidigital number, since it uses as much as digits as its factorization.

2809856561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 517950.

The product of its (nonzero) digits is 1036800, while the sum is 50.

The square root of 2809856561 is about 53008.0801482189. The cubic root of 2809856561 is about 1411.1116697938. Note that the first 3 decimals are identical.

The spelling of 2809856561 in words is "two billion, eight hundred nine million, eight hundred fifty-six thousand, five hundred sixty-one".