81559840 has 96 divisors (see below), whose sum is σ = 206841600. Its totient is φ = 30311424.

The previous prime is 81559813. The next prime is 81559843. The reversal of 81559840 is 4895518.

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 = 81559793 and 81559802.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81559843) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 135861 + ... + 136459.

It is an arithmetic number, because the mean of its divisors is an integer number (2154600).

It is a vampire number, since it can be written as 8510 ⋅ 9584 (with its own digits).

Almost surely, 2^81559840 is an apocalyptic number.

81559840 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 81559840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (103420800).

81559840 is an abundant number, since it is smaller than the sum of its proper divisors (125281760).

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

81559840 is a wasteful number, since it uses less digits than its factorization.

81559840 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 674 (or 666 counting only the distinct ones).

The product of its (nonzero) digits is 57600, while the sum is 40.

The square root of 81559840 is about 9031.0486655759. The cubic root of 81559840 is about 433.6694092396.

The spelling of 81559840 in words is "eighty-one million, five hundred fifty-nine thousand, eight hundred forty".