81861 has 8 divisors (see below), whose sum is σ = 117600. Its totient is φ = 50352.

The previous prime is 81853. The next prime is 81869. The reversal of 81861 is 16818.

81861 = T₆₆ + T₆₇ + ... + T₉₁.

It is an interprime number because it is at equal distance from previous prime (81853) and next prime (81869).

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 81861 - 2³ = 81853 is a prime.

81861 is a lucky number.

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 81861.

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 in 7 ways as a sum of consecutive naturals, for example, 1011 + ... + 1088.

It is an arithmetic number, because the mean of its divisors is an integer number (14700).

2⁸¹⁸⁶¹ is an apocalyptic number.

It is an amenable number.

81861 is a deficient number, since it is larger than the sum of its proper divisors (35739).

81861 is a wasteful number, since it uses less digits than its factorization.

81861 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2115.

The product of its digits is 384, while the sum is 24.

The square root of 81861 is about 286.1136137970. The cubic root of 81861 is about 43.4202528875.

The spelling of 81861 in words is "eighty-one thousand, eight hundred sixty-one".