666856 has 8 divisors (see below), whose sum is σ = 1250370. Its totient is φ = 333424.

The previous prime is 666829. The next prime is 666857. The reversal of 666856 is 658666.

It can be written as a sum of positive squares in only one way, i.e., 532900 + 133956 = 730^2 + 366^2 .

It is a tau number, because it is divible by the number of its divisors (8).

It is not an unprimeable number, because it can be changed into a prime (666857) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 41671 + ... + 41686.

2⁶⁶⁶⁸⁵⁶ is an apocalyptic number.

It is an amenable number.

666856 is a deficient number, since it is larger than the sum of its proper divisors (583514).

666856 is a wasteful number, since it uses less digits than its factorization.

666856 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 83363 (or 83359 counting only the distinct ones).

The product of its digits is 51840, while the sum is 37.

The square root of 666856 is about 816.6125152115. The cubic root of 666856 is about 87.3663155859.

It can be divided in two parts, 6668 and 56, that added together give a square (6724 = 82²).

The spelling of 666856 in words is "six hundred sixty-six thousand, eight hundred fifty-six".