81806205 has 32 divisors (see below), whose sum is σ = 142361856. Its totient is φ = 39873024.

The previous prime is 81806203. The next prime is 81806251. The reversal of 81806205 is 50260818.

It is not a de Polignac number, because 81806205 - 2¹ = 81806203 is a prime.

It is a Smith number, since the sum of its digits (30) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81806203) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 18049 + ... + 22121.

It is an arithmetic number, because the mean of its divisors is an integer number (4448808).

Almost surely, 2^81806205 is an apocalyptic number.

It is an amenable number.

81806205 is a deficient number, since it is larger than the sum of its proper divisors (60555651).

81806205 is a wasteful number, since it uses less digits than its factorization.

81806205 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4197.

The product of its (nonzero) digits is 3840, while the sum is 30.

The square root of 81806205 is about 9044.6782695682. The cubic root of 81806205 is about 434.1056270614.

The spelling of 81806205 in words is "eighty-one million, eight hundred six thousand, two hundred five".