665851 has 4 divisors (see below), whose sum is σ = 668304. Its totient is φ = 663400.

The previous prime is 665843. The next prime is 665857. The reversal of 665851 is 158566.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 158566 = 2 ⋅79283.

It is a cyclic number.

It is not a de Polignac number, because 665851 - 2³ = 665843 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (665857) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 760 + ... + 1381.

It is an arithmetic number, because the mean of its divisors is an integer number (167076).

2⁶⁶⁵⁸⁵¹ is an apocalyptic number.

665851 is a deficient number, since it is larger than the sum of its proper divisors (2453).

665851 is a wasteful number, since it uses less digits than its factorization.

665851 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2452.

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

The square root of 665851 is about 815.9969362688. The cubic root of 665851 is about 87.3224044104.

The spelling of 665851 in words is "six hundred sixty-five thousand, eight hundred fifty-one".