81665808 has 80 divisors (see below), whose sum is σ = 247662720. Its totient is φ = 22699008.

The previous prime is 81665797. The next prime is 81665851. The reversal of 81665808 is 80856618.

It is a Harshad number since it is a multiple of its sum of digits (42).

It is a self number, because there is not a number n which added to its sum of digits gives 81665808.

It is an unprimeable number.

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 15 ways as a sum of consecutive naturals, for example, 9148 + ... + 15716.

It is an arithmetic number, because the mean of its divisors is an integer number (3095784).

Almost surely, 2^81665808 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 81665808, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (123831360).

81665808 is an abundant number, since it is smaller than the sum of its proper divisors (165996912).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

81665808 is a wasteful number, since it uses less digits than its factorization.

81665808 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6624 (or 6618 counting only the distinct ones).

The product of its (nonzero) digits is 92160, while the sum is 42.

The square root of 81665808 is about 9036.9136324300. The cubic root of 81665808 is about 433.8571453921.

The spelling of 81665808 in words is "eighty-one million, six hundred sixty-five thousand, eight hundred eight".