81129664 has 112 divisors (see below), whose sum is σ = 203947776. Its totient is φ = 31104000.

The previous prime is 81129623. The next prime is 81129679. The reversal of 81129664 is 46692118.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (112).

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, 497647 + ... + 497809.

Almost surely, 2^81129664 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 81129664, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (101973888).

81129664 is an abundant number, since it is smaller than the sum of its proper divisors (122818112).

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

81129664 is a wasteful number, since it uses less digits than its factorization.

81129664 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 294 (or 284 counting only the distinct ones).

The product of its digits is 20736, while the sum is 37.

The square root of 81129664 is about 9007.2006750155. The cubic root of 81129664 is about 432.9056218949.

The spelling of 81129664 in words is "eighty-one million, one hundred twenty-nine thousand, six hundred sixty-four".