• 866 can be written using four 4's:

866 has 4 divisors (see below), whose sum is σ = 1302. Its totient is φ = 432.

The previous prime is 863. The next prime is 877. The reversal of 866 is 668.

866 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

866 is an esthetic number in base 7, because in such base its adjacent digits differ by 1.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in only one way, i.e., 841 + 25 = 29^2 + 5^2 .

It is an Ulam number.

866 is a modest number, since divided by 66 gives 8 as remainder.

It is a Curzon number.

It is a plaindrome in base 7 and base 14.

It is a nialpdrome in base 10.

It is a congruent number.

It is an inconsummate number, since it does not exist a number *n* which divided by its sum of digits gives 866.

It is not an unprimeable number, because it can be changed into a prime (863) by changing a digit.

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 as a sum of consecutive naturals, namely, 215 + ... + 218.

2^{866} is an apocalyptic number.

866 is a deficient number, since it is larger than the sum of its proper divisors (436).

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

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

The sum of its prime factors is 435.

The product of its digits is 288, while the sum is 20.

The square root of 866 is about 29.4278779391. The cubic root of 866 is about 9.5317497274.

It can be divided in two parts, 8 and 66, that multiplied together give a triangular number (528 = T_{32}).

The spelling of 866 in words is "eight hundred sixty-six", and thus it is an aban number and an oban number.

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