851661 has 8 divisors (see below), whose sum is σ = 1261760. Its totient is φ = 567756.

The previous prime is 851659. The next prime is 851671. The reversal of 851661 is 166158.

It is not a de Polignac number, because 851661 - 2¹ = 851659 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27), and also a Moran number because the ratio is a prime number: 31543 = 851661 / (8 + 5 + 1 + 6 + 6 + 1).

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (851671) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 15745 + ... + 15798.

It is an arithmetic number, because the mean of its divisors is an integer number (157720).

2⁸⁵¹⁶⁶¹ is an apocalyptic number.

It is an amenable number.

851661 is a deficient number, since it is larger than the sum of its proper divisors (410099).

851661 is a wasteful number, since it uses less digits than its factorization.

851661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 31552 (or 31546 counting only the distinct ones).

The product of its digits is 1440, while the sum is 27.

The square root of 851661 is about 922.8548098157. The cubic root of 851661 is about 94.7884860235.

The spelling of 851661 in words is "eight hundred fifty-one thousand, six hundred sixty-one".