81665120205 has 12 divisors (see below), whose sum is σ = 141552875100. Its totient is φ = 43554730752.

The previous prime is 81665120189. The next prime is 81665120233. The reversal of 81665120205 is 50202156618.

81665120205 is a `hidden beast` number, since 81 + 66 + 512 + 0 + 2 + 0 + 5 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 65112239241 + 16552880964 = 255171^2 + 128658^2 .

It is not a de Polignac number, because 81665120205 - 2⁴ = 81665120189 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 81665120205.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 907390180 + ... + 907390269.

It is an arithmetic number, because the mean of its divisors is an integer number (11796072925).

Almost surely, 2^81665120205 is an apocalyptic number.

It is an amenable number.

81665120205 is a deficient number, since it is larger than the sum of its proper divisors (59887754895).

81665120205 is a wasteful number, since it uses less digits than its factorization.

81665120205 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1814780460 (or 1814780457 counting only the distinct ones).

The product of its (nonzero) digits is 28800, while the sum is 36.

The spelling of 81665120205 in words is "eighty-one billion, six hundred sixty-five million, one hundred twenty thousand, two hundred five".