81891584 has 72 divisors (see below), whose sum is σ = 178956288. Its totient is φ = 37232640.

The previous prime is 81891583. The next prime is 81891599. The reversal of 81891584 is 48519818.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81891581) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 134609 + ... + 135215.

It is an arithmetic number, because the mean of its divisors is an integer number (2485504).

Almost surely, 2^81891584 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 81891584, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (89478144).

81891584 is an abundant number, since it is smaller than the sum of its proper divisors (97064704).

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

81891584 is a wasteful number, since it uses less digits than its factorization.

81891584 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 671 (or 657 counting only the distinct ones).

The product of its digits is 92160, while the sum is 44.

The square root of 81891584 is about 9049.3968859809. The cubic root of 81891584 is about 434.2565961218.

The spelling of 81891584 in words is "eighty-one million, eight hundred ninety-one thousand, five hundred eighty-four".