81440 has 24 divisors (see below), whose sum is σ = 192780. Its totient is φ = 32512.

The previous prime is 81439. The next prime is 81457. The reversal of 81440 is 4418.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 80656 + 784 = 284^2 + 28^2 .

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 81440.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 95 + ... + 414.

2⁸¹⁴⁴⁰ is an apocalyptic number.

81440 is a gapful number since it is divisible by the number (80) formed by its first and last digit.

It is an amenable number.

81440 is an abundant number, since it is smaller than the sum of its proper divisors (111340).

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

It is a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (96390).

81440 is a wasteful number, since it uses less digits than its factorization.

81440 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 524 (or 516 counting only the distinct ones).

The product of its (nonzero) digits is 128, while the sum is 17.

The square root of 81440 is about 285.3769437078. The cubic root of 81440 is about 43.3456900987.

Adding to 81440 its reverse (4418), we get a palindrome (85858).

The spelling of 81440 in words is "eighty-one thousand, four hundred forty".