856561 has 4 divisors (see below), whose sum is σ = 884224. Its totient is φ = 828900.

The previous prime is 856553. The next prime is 856567. The reversal of 856561 is 165658.

856561 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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 856561 - 2³ = 856553 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (31), and also a Moran number because the ratio is a prime number: 27631 = 856561 / (8 + 5 + 6 + 5 + 6 + 1).

It is an alternating number because its digits alternate between even and odd.

It is a Duffinian number.

856561 is a lucky number.

It is not an unprimeable number, because it can be changed into a prime (856567) 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, 13785 + ... + 13846.

It is an arithmetic number, because the mean of its divisors is an integer number (221056).

2⁸⁵⁶⁵⁶¹ is an apocalyptic number.

It is an amenable number.

856561 is a deficient number, since it is larger than the sum of its proper divisors (27663).

856561 is a wasteful number, since it uses less digits than its factorization.

856561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 27662.

The product of its digits is 7200, while the sum is 31.

The square root of 856561 is about 925.5058076533. The cubic root of 856561 is about 94.9699258452.

The spelling of 856561 in words is "eight hundred fifty-six thousand, five hundred sixty-one".