81608809 has 4 divisors (see below), whose sum is σ = 81797716. Its totient is φ = 81419904.

The previous prime is 81608777. The next prime is 81608827. The reversal of 81608809 is 90880618.

It is a happy number.

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 46621584 + 34987225 = 6828^2 + 5915^2 .

It is a cyclic number.

It is not a de Polignac number, because 81608809 - 2⁵ = 81608777 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81608869) 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, 93804 + ... + 94669.

It is an arithmetic number, because the mean of its divisors is an integer number (20449429).

Almost surely, 2^81608809 is an apocalyptic number.

It is an amenable number.

81608809 is a deficient number, since it is larger than the sum of its proper divisors (188907).

81608809 is a wasteful number, since it uses less digits than its factorization.

81608809 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 188906.

The product of its (nonzero) digits is 27648, while the sum is 40.

The square root of 81608809 is about 9033.7594056959. The cubic root of 81608809 is about 433.7561844163.

The spelling of 81608809 in words is "eighty-one million, six hundred eight thousand, eight hundred nine".