81664128 has 384 divisors, whose sum is σ = 311875200. Its totient is φ = 19906560.

The previous prime is 81664127. The next prime is 81664139. The reversal of 81664128 is 82146618.

81664128 is a `hidden beast` number, since 8 + 1 + 6 + 641 + 2 + 8 = 666.

It is a tau number, because it is divible by the number of its divisors (384).

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a nude number because it is divisible by every one of its digits.

It is a junction number, because it is equal to n+sod(n) for n = 81664092 and 81664101.

It is not an unprimeable number, because it can be changed into a prime (81664127) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 1991788 + ... + 1991828.

It is an arithmetic number, because the mean of its divisors is an integer number (812175).

Almost surely, 2^81664128 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 81664128, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (155937600).

81664128 is an abundant number, since it is smaller than the sum of its proper divisors (230211072).

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

81664128 is a wasteful number, since it uses less digits than its factorization.

81664128 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 100 (or 85 counting only the distinct ones).

The product of its digits is 18432, while the sum is 36.

The square root of 81664128 is about 9036.8206798630. The cubic root of 81664128 is about 433.8541703200.

The spelling of 81664128 in words is "eighty-one million, six hundred sixty-four thousand, one hundred twenty-eight".