16856561 has 4 divisors (see below), whose sum is σ = 16882800. Its totient is φ = 16830324.

The previous prime is 16856533. The next prime is 16856573. The reversal of 16856561 is 16565861.

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: 16565861 = 13 ⋅1274297.

It is a cyclic number.

It is not a de Polignac number, because 16856561 - 2²² = 12662257 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (16856501) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 12131 + ... + 13448.

It is an arithmetic number, because the mean of its divisors is an integer number (4220700).

Almost surely, 2^16856561 is an apocalyptic number.

It is an amenable number.

16856561 is a deficient number, since it is larger than the sum of its proper divisors (26239).

16856561 is an equidigital number, since it uses as much as digits as its factorization.

16856561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 26238.

The product of its digits is 43200, while the sum is 38.

The square root of 16856561 is about 4105.6742442624. The cubic root of 16856561 is about 256.4029350011.

The spelling of 16856561 in words is "sixteen million, eight hundred fifty-six thousand, five hundred sixty-one".