81181440 has 288 divisors, whose sum is σ = 301694400. Its totient is φ = 20901888.

The previous prime is 81181393. The next prime is 81181447. The reversal of 81181440 is 4418118.

It is a tau number, because it is divible by the number of its divisors (288).

It is a Harshad number since it is a multiple of its sum of digits (27).

It is not an unprimeable number, because it can be changed into a prime (81181447) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 2799346 + ... + 2799374.

It is an arithmetic number, because the mean of its divisors is an integer number (1047550).

Almost surely, 2^81181440 is an apocalyptic number.

81181440 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 81181440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (150847200).

81181440 is an abundant number, since it is smaller than the sum of its proper divisors (220512960).

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

81181440 is an frugal number, since it uses more digits than its factorization.

81181440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 71 (or 39 counting only the distinct ones).

The product of its (nonzero) digits is 1024, while the sum is 27.

The square root of 81181440 is about 9010.0743615133. The cubic root of 81181440 is about 432.9976940747.

Adding to 81181440 its reverse (4418118), we get a palindrome (85599558).

The spelling of 81181440 in words is "eighty-one million, one hundred eighty-one thousand, four hundred forty".