81066809 has 4 divisors (see below), whose sum is σ = 81100404. Its totient is φ = 81033216.

The previous prime is 81066763. The next prime is 81066841. The reversal of 81066809 is 90866018.

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

It can be written as a sum of positive squares in 2 ways, for example, as 80496784 + 570025 = 8972^2 + 755^2 .

It is a cyclic number.

It is not a de Polignac number, because 81066809 - 2²⁰ = 80018233 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (81066859) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 12872 + ... + 18105.

It is an arithmetic number, because the mean of its divisors is an integer number (20275101).

Almost surely, 2^81066809 is an apocalyptic number.

It is an amenable number.

81066809 is a deficient number, since it is larger than the sum of its proper divisors (33595).

81066809 is a wasteful number, since it uses less digits than its factorization.

81066809 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 33594.

The product of its (nonzero) digits is 20736, while the sum is 38.

The square root of 81066809 is about 9003.7108460901. The cubic root of 81066809 is about 432.7937955025.

The spelling of 81066809 in words is "eighty-one million, sixty-six thousand, eight hundred nine".