81309 has 4 divisors (see below), whose sum is σ = 108416. Its totient is φ = 54204.

The previous prime is 81307. The next prime is 81331. The reversal of 81309 is 90318.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is not a de Polignac number, because 81309 - 2¹ = 81307 is a prime.

It is a super-2 number, since 2×81309² = 13222306962, which contains 22 as substring.

It is a D-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 (81307) 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, 13549 + ... + 13554.

It is an arithmetic number, because the mean of its divisors is an integer number (27104).

2⁸¹³⁰⁹ is an apocalyptic number.

It is an amenable number.

81309 is a deficient number, since it is larger than the sum of its proper divisors (27107).

81309 is a wasteful number, since it uses less digits than its factorization.

81309 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 27106.

The product of its (nonzero) digits is 216, while the sum is 21.

The square root of 81309 is about 285.1473303399. The cubic root of 81309 is about 43.3224364448.

Subtracting 81309 from its reverse (90318), we obtain a palindrome (9009).

The spelling of 81309 in words is "eighty-one thousand, three hundred nine".