81606865 has 4 divisors (see below), whose sum is σ = 97928244. Its totient is φ = 65285488.

The previous prime is 81606857. The next prime is 81606869. The reversal of 81606865 is 56860618.

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 9628609 + 71978256 = 3103^2 + 8484^2 .

It is a cyclic number.

It is not a de Polignac number, because 81606865 - 2³ = 81606857 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81606869) 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, 8160682 + ... + 8160691.

It is an arithmetic number, because the mean of its divisors is an integer number (24482061).

Almost surely, 2^81606865 is an apocalyptic number.

It is an amenable number.

81606865 is a deficient number, since it is larger than the sum of its proper divisors (16321379).

81606865 is a wasteful number, since it uses less digits than its factorization.

81606865 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16321378.

The product of its (nonzero) digits is 69120, while the sum is 40.

The square root of 81606865 is about 9033.6518086541. The cubic root of 81606865 is about 433.7527402264.

The spelling of 81606865 in words is "eighty-one million, six hundred six thousand, eight hundred sixty-five".