81664 has 36 divisors (see below), whose sum is σ = 183960. Its totient is φ = 35840.

The previous prime is 81649. The next prime is 81667. The reversal of 81664 is 46618.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81667) by changing a digit.

81664 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2802 + ... + 2830.

It is an arithmetic number, because the mean of its divisors is an integer number (5110).

2⁸¹⁶⁶⁴ 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 81664, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (91980).

81664 is an abundant number, since it is smaller than the sum of its proper divisors (102296).

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

81664 is a wasteful number, since it uses less digits than its factorization.

81664 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 56 (or 42 counting only the distinct ones).

The product of its digits is 1152, while the sum is 25.

The square root of 81664 is about 285.7691375919. The cubic root of 81664 is about 43.3853943646.

The spelling of 81664 in words is "eighty-one thousand, six hundred sixty-four".