81665686815 has 16 divisors (see below), whose sum is σ = 130717909728. Its totient is φ = 43537429376.

The previous prime is 81665686799. The next prime is 81665686819. The reversal of 81665686815 is 51868656618.

It is a cyclic number.

It is not a de Polignac number, because 81665686815 - 2⁴ = 81665686799 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81665686819) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 1061832 + ... + 1136141.

It is an arithmetic number, because the mean of its divisors is an integer number (8169869358).

Almost surely, 2^81665686815 is an apocalyptic number.

81665686815 is a deficient number, since it is larger than the sum of its proper divisors (49052222913).

81665686815 is a wasteful number, since it uses less digits than its factorization.

81665686815 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2200458.

The product of its digits is 16588800, while the sum is 60.

The spelling of 81665686815 in words is "eighty-one billion, six hundred sixty-five million, six hundred eighty-six thousand, eight hundred fifteen".