81689904 has 80 divisors (see below), whose sum is σ = 235699200. Its totient is φ = 27088704.

The previous prime is 81689869. The next prime is 81689921. The reversal of 81689904 is 40998618.

It is a Smith number, since the sum of its digits (45) coincides with the sum of the digits of its prime factors.

It is a self number, because there is not a number n which added to its sum of digits gives 81689904.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 113257 + ... + 113975.

It is an arithmetic number, because the mean of its divisors is an integer number (2946240).

Almost surely, 2^81689904 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 81689904, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (117849600).

81689904 is an abundant number, since it is smaller than the sum of its proper divisors (154009296).

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

81689904 is a wasteful number, since it uses less digits than its factorization.

81689904 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 999 (or 987 counting only the distinct ones).

The product of its (nonzero) digits is 124416, while the sum is 45.

The square root of 81689904 is about 9038.2467326357. The cubic root of 81689904 is about 433.8998119377.

The spelling of 81689904 in words is "eighty-one million, six hundred eighty-nine thousand, nine hundred four".