81664440 has 128 divisors (see below), whose sum is σ = 287884800. Its totient is φ = 18270720.

The previous prime is 81664423. The next prime is 81664441. The reversal of 81664440 is 4446618.

It is a Harshad number since it is a multiple of its sum of digits (33).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81664441) 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, 14781 + ... + 19539.

It is an arithmetic number, because the mean of its divisors is an integer number (2249100).

Almost surely, 2^81664440 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 81664440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (143942400).

81664440 is an abundant number, since it is smaller than the sum of its proper divisors (206220360).

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

81664440 is a wasteful number, since it uses less digits than its factorization.

81664440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4797 (or 4793 counting only the distinct ones).

The product of its (nonzero) digits is 18432, while the sum is 33.

The square root of 81664440 is about 9036.8379425549. The cubic root of 81664440 is about 433.8547228365.

It can be divided in two parts, 816 and 64440, that added together give a palindrome (65256).

The spelling of 81664440 in words is "eighty-one million, six hundred sixty-four thousand, four hundred forty".