81685805 has 4 divisors (see below), whose sum is σ = 98022972. Its totient is φ = 65348640.

The previous prime is 81685789. The next prime is 81685819. The reversal of 81685805 is 50858618.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 50858618 = 2 ⋅25429309.

It can be written as a sum of positive squares in 2 ways, for example, as 29571844 + 52113961 = 5438^2 + 7219^2 .

It is not a de Polignac number, because 81685805 - 2⁴ = 81685789 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 8168576 + ... + 8168585.

It is an arithmetic number, because the mean of its divisors is an integer number (24505743).

Almost surely, 2^81685805 is an apocalyptic number.

It is an amenable number.

81685805 is a deficient number, since it is larger than the sum of its proper divisors (16337167).

81685805 is a wasteful number, since it uses less digits than its factorization.

81685805 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16337166.

The product of its (nonzero) digits is 76800, while the sum is 41.

The square root of 81685805 is about 9038.0199712105. The cubic root of 81685805 is about 433.8925544718.

The spelling of 81685805 in words is "eighty-one million, six hundred eighty-five thousand, eight hundred five".