81709 has 4 divisors (see below), whose sum is σ = 82620.
Its totient is φ = 80800.
The previous prime is 81707. The next prime is 81727. The reversal of 81709 is 90718.
Subtracting 81709 from its reverse (90718), we obtain a palindrome (9009).
It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.
It can be written as a sum of positive squares in 2 ways, for example, as 75625 + 6084 = 275^2 + 78^2
It is not a de Polignac number, because 81709 - 21 = 81707 is a prime.
It is a Duffinian number.
It is a congruent number.
It is not an unprimeable number, because it can be changed into a prime (81701) 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, 304 + ... + 505.
It is an arithmetic number, because the mean of its divisors is an integer number (20655).
281709 is an apocalyptic number.
It is an amenable number.
81709 is a deficient number, since it is larger than the sum of its proper divisors (911).
81709 is a wasteful number, since it uses less digits than its factorization.
81709 is an odious number, because the sum of its binary digits is odd.
The sum of its prime factors is 910.
The product of its (nonzero) digits is 504, while the sum is 25.
The square root of 81709 is about 285.8478616327.
The cubic root of 81709 is about 43.3933619074.
The spelling of 81709 in words is "eighty-one thousand, seven hundred nine".