81388665 has 32 divisors (see below), whose sum is σ = 146044800. Its totient is φ = 43001280.

The previous prime is 81388633. The next prime is 81388669. The reversal of 81388665 is 56688318.

It is not a de Polignac number, because 81388665 - 2⁵ = 81388633 is a prime.

It is a super-2 number, since 2×81388665² = 13248229580964450, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (45).

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 81388665.

It is not an unprimeable number, because it can be changed into a prime (81388669) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 11950 + ... + 17480.

It is an arithmetic number, because the mean of its divisors is an integer number (4563900).

Almost surely, 2^81388665 is an apocalyptic number.

It is an amenable number.

81388665 is a deficient number, since it is larger than the sum of its proper divisors (64656135).

81388665 is a wasteful number, since it uses less digits than its factorization.

81388665 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5654 (or 5648 counting only the distinct ones).

The product of its digits is 276480, while the sum is 45.

The square root of 81388665 is about 9021.5666599544. The cubic root of 81388665 is about 433.3658065737.

The spelling of 81388665 in words is "eighty-one million, three hundred eighty-eight thousand, six hundred sixty-five".