856640561 has 4 divisors (see below), whose sum is σ = 979017792. Its totient is φ = 734263332.

The previous prime is 856640549. The next prime is 856640573. The reversal of 856640561 is 165046658.

It is a happy number.

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 an interprime number because it is at equal distance from previous prime (856640549) and next prime (856640573).

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-856640561 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (856640531) 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, 61188605 + ... + 61188618.

It is an arithmetic number, because the mean of its divisors is an integer number (244754448).

Almost surely, 2^856640561 is an apocalyptic number.

It is an amenable number.

856640561 is a deficient number, since it is larger than the sum of its proper divisors (122377231).

856640561 is a wasteful number, since it uses less digits than its factorization.

856640561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 122377230.

The product of its (nonzero) digits is 172800, while the sum is 41.

The square root of 856640561 is about 29268.4225915918. The cubic root of 856640561 is about 949.7286615660.

The spelling of 856640561 in words is "eight hundred fifty-six million, six hundred forty thousand, five hundred sixty-one".