665856 has 81 divisors (see below), whose sum is σ = 2039401. Its totient is φ = 208896.

The previous prime is 665843. The next prime is 665857. The reversal of 665856 is 658566.

The square root of 665856 is 816.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in only one way, i.e., 518400 + 147456 = 720^2 + 384^2 .

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 665856.

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

665856 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 39160 + ... + 39176.

2⁶⁶⁵⁸⁵⁶ is an apocalyptic number.

665856 is the 816-th square number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 665856

665856 is an abundant number, since it is smaller than the sum of its proper divisors (1373545).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

665856 is a wasteful number, since it uses less digits than its factorization.

665856 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 56 (or 22 counting only the distinct ones).

The product of its digits is 43200, while the sum is 36.

The cubic root of 665856 is about 87.3226229833.

Multiplying 665856 by its sum of digits (36), we get a square (23970816 = 4896²).

665856 divided by its sum of digits (36) gives a square (18496 = 136²).

It can be divided in two parts, 665 and 856, that added together give a square (1521 = 39²).

The spelling of 665856 in words is "six hundred sixty-five thousand, eight hundred fifty-six".