851561 has 4 divisors (see below), whose sum is σ = 896400. Its totient is φ = 806724.

The previous prime is 851549. The next prime is 851569. The reversal of 851561 is 165158.

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 851561 - 2¹⁰ = 850537 is a prime.

It is a super-2 number, since 2×851561² = 1450312273442, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 851561.

It is not an unprimeable number, because it can be changed into a prime (851569) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 22391 + ... + 22428.

It is an arithmetic number, because the mean of its divisors is an integer number (224100).

2⁸⁵¹⁵⁶¹ is an apocalyptic number.

It is an amenable number.

851561 is a deficient number, since it is larger than the sum of its proper divisors (44839).

851561 is a wasteful number, since it uses less digits than its factorization.

851561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 44838.

The product of its digits is 1200, while the sum is 26.

The square root of 851561 is about 922.8006285217. The cubic root of 851561 is about 94.7847759324.

The spelling of 851561 in words is "eight hundred fifty-one thousand, five hundred sixty-one".