81009 has 6 divisors (see below), whose sum is σ = 117026. Its totient is φ = 54000.

The previous prime is 81001. The next prime is 81013. The reversal of 81009 is 90018.

81009 is nontrivially palindromic in base 11.

It can be written as a sum of positive squares in only one way, i.e., 57600 + 23409 = 240^2 + 153^2 .

It is not a de Polignac number, because 81009 - 2³ = 81001 is a prime.

It is an Ulam number.

It is a Duffinian number.

81009 is a lucky number.

It is a junction number, because it is equal to n+sod(n) for n = 80982 and 81000.

It is not an unprimeable number, because it can be changed into a prime (81001) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 4492 + ... + 4509.

2⁸¹⁰⁰⁹ is an apocalyptic number.

It is an amenable number.

81009 is a deficient number, since it is larger than the sum of its proper divisors (36017).

81009 is a wasteful number, since it uses less digits than its factorization.

81009 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9007 (or 9004 counting only the distinct ones).

The product of its (nonzero) digits is 72, while the sum is 18.

The square root of 81009 is about 284.6208003643. The cubic root of 81009 is about 43.2690895494.

Subtracting 81009 from its reverse (90018), we obtain a palindrome (9009).

It can be divided in two parts, 8100 and 9, that multiplied together give a square (72900 = 270²).

The spelling of 81009 in words is "eighty-one thousand, nine".