81739 has 4 divisors (see below), whose sum is σ = 93424. Its totient is φ = 70056.

The previous prime is 81737. The next prime is 81749. The reversal of 81739 is 93718.

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

It is not a de Polignac number, because 81739 - 2¹ = 81737 is a prime.

It is an Ulam number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81737) 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 3 ways as a sum of consecutive naturals, for example, 5832 + ... + 5845.

It is an arithmetic number, because the mean of its divisors is an integer number (23356).

2⁸¹⁷³⁹ is an apocalyptic number.

81739 is a deficient number, since it is larger than the sum of its proper divisors (11685).

81739 is a wasteful number, since it uses less digits than its factorization.

81739 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 11684.

The product of its digits is 1512, while the sum is 28.

The square root of 81739 is about 285.9003322838. The cubic root of 81739 is about 43.3986719776.

It can be divided in two parts, 81 and 739, that added together give a triangular number (820 = T₄₀).

The spelling of 81739 in words is "eighty-one thousand, seven hundred thirty-nine".