81599440 has 80 divisors (see below), whose sum is σ = 210986496. Its totient is φ = 29145600.

The previous prime is 81599437. The next prime is 81599459. The reversal of 81599440 is 4499518.

It is a tau number, because it is divible by the number of its divisors (80).

It is a Harshad number since it is a multiple of its sum of digits (40).

It is a junction number, because it is equal to n+sod(n) for n = 81599393 and 81599402.

It is a congruent number.

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, 30975 + ... + 33505.

Almost surely, 2^81599440 is an apocalyptic number.

81599440 is a gapful number since it is divisible by the number (80) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 81599440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (105493248).

81599440 is an abundant number, since it is smaller than the sum of its proper divisors (129387056).

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

81599440 is a wasteful number, since it uses less digits than its factorization.

81599440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2588 (or 2582 counting only the distinct ones).

The product of its (nonzero) digits is 51840, while the sum is 40.

The square root of 81599440 is about 9033.2408359348. The cubic root of 81599440 is about 433.7395848308.

The spelling of 81599440 in words is "eighty-one million, five hundred ninety-nine thousand, four hundred forty".