81231840 has 144 divisors (see below), whose sum is σ = 291891600. Its totient is φ = 20514816.

The previous prime is 81231823. The next prime is 81231841. The reversal of 81231840 is 4813218.

It is a tau number, because it is divible by the number of its divisors (144).

It is a super-2 number, since 2×81231840² = 13197223659571200, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81231841) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 25876 + ... + 28844.

It is an arithmetic number, because the mean of its divisors is an integer number (2027025).

Almost surely, 2^81231840 is an apocalyptic number.

81231840 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 81231840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (145945800).

81231840 is an abundant number, since it is smaller than the sum of its proper divisors (210659760).

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

81231840 is a wasteful number, since it uses less digits than its factorization.

81231840 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3009 (or 2998 counting only the distinct ones).

The product of its (nonzero) digits is 1536, while the sum is 27.

The square root of 81231840 is about 9012.8707968105. The cubic root of 81231840 is about 433.0872817488.

The spelling of 81231840 in words is "eighty-one million, two hundred thirty-one thousand, eight hundred forty".