16856509 has 4 divisors (see below), whose sum is σ = 16867360. Its totient is φ = 16845660.

The previous prime is 16856501. The next prime is 16856513. The reversal of 16856509 is 90565861.

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 a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 90565861 = 509 ⋅177929.

It is a cyclic number.

It is not a de Polignac number, because 16856509 - 2³ = 16856501 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (16856501) 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, 2607 + ... + 6364.

It is an arithmetic number, because the mean of its divisors is an integer number (4216840).

Almost surely, 2^16856509 is an apocalyptic number.

It is an amenable number.

16856509 is a deficient number, since it is larger than the sum of its proper divisors (10851).

16856509 is an equidigital number, since it uses as much as digits as its factorization.

16856509 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10850.

The product of its (nonzero) digits is 64800, while the sum is 40.

The square root of 16856509 is about 4105.6679115584. The cubic root of 16856509 is about 256.4026713458.

The spelling of 16856509 in words is "sixteen million, eight hundred fifty-six thousand, five hundred nine".