665855 has 16 divisors (see below), whose sum is σ = 865920. Its totient is φ = 489888.

The previous prime is 665843. The next prime is 665857. The reversal of 665855 is 558566.

It is a Cunningham number, because it is equal to 816²-1.

It is a cyclic number.

It is not a de Polignac number, because 665855 - 2¹⁴ = 649471 is a prime.

665855 is a modest number, since divided by 855 gives 665 as remainder.

It is a congruent number.

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

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 4004 + ... + 4166.

It is an arithmetic number, because the mean of its divisors is an integer number (54120).

2⁶⁶⁵⁸⁵⁵ is an apocalyptic number.

665855 is a deficient number, since it is larger than the sum of its proper divisors (200065).

665855 is a wasteful number, since it uses less digits than its factorization.

665855 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 230.

The product of its digits is 36000, while the sum is 35.

The square root of 665855 is about 815.9993872547. Note that the first 3 decimals coincide. The cubic root of 665855 is about 87.3225792688.

The spelling of 665855 in words is "six hundred sixty-five thousand, eight hundred fifty-five".