81866 has 4 divisors (see below), whose sum is σ = 122802. Its totient is φ = 40932.

The previous prime is 81853. The next prime is 81869. The reversal of 81866 is 66818.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 66818 = 2 ⋅33409.

It can be written as a sum of positive squares in only one way, i.e., 75625 + 6241 = 275^2 + 79^2 .

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (81869) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 20465 + ... + 20468.

2⁸¹⁸⁶⁶ is an apocalyptic number.

81866 is a deficient number, since it is larger than the sum of its proper divisors (40936).

81866 is a wasteful number, since it uses less digits than its factorization.

81866 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 40935.

The product of its digits is 2304, while the sum is 29.

The square root of 81866 is about 286.1223514513. The cubic root of 81866 is about 43.4211368935.

It can be divided in two parts, 8186 and 6, that added together give a 13-th power (8192 = 2¹³).

The spelling of 81866 in words is "eighty-one thousand, eight hundred sixty-six".