866781 has 28 divisors (see below), whose sum is σ = 1377180. Its totient is φ = 544320.

The previous prime is 866777. The next prime is 866783. The reversal of 866781 is 187668.

It can be written as a sum of positive squares in 2 ways, for example, as 210681 + 656100 = 459^2 + 810^2 .

It is not a de Polignac number, because 866781 - 2² = 866777 is a prime.

It is a super-2 number, since 2×866781² = 1502618603922, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (866783) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 27 ways as a sum of consecutive naturals, for example, 21121 + ... + 21161.

It is an arithmetic number, because the mean of its divisors is an integer number (49185).

2⁸⁶⁶⁷⁸¹ is an apocalyptic number.

866781 is a gapful number since it is divisible by the number (81) formed by its first and last digit.

It is an amenable number.

866781 is a deficient number, since it is larger than the sum of its proper divisors (510399).

866781 is an equidigital number, since it uses as much as digits as its factorization.

866781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 88 (or 73 counting only the distinct ones).

The product of its digits is 16128, while the sum is 36.

The square root of 866781 is about 931.0107410766. The cubic root of 866781 is about 95.3461426162.

The spelling of 866781 in words is "eight hundred sixty-six thousand, seven hundred eighty-one".