81858640 has 40 divisors (see below), whose sum is σ = 192476520. Its totient is φ = 32372736.

The previous prime is 81858613. The next prime is 81858641. The reversal of 81858640 is 4685818.

It can be written as a sum of positive squares in 4 ways, for example, as 3429904 + 78428736 = 1852^2 + 8856^2 .

It is a tau number, because it is divible by the number of its divisors (40).

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 = 81858593 and 81858602.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81858641) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1372 + ... + 12868.

It is an arithmetic number, because the mean of its divisors is an integer number (4811913).

Almost surely, 2^81858640 is an apocalyptic number.

81858640 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 81858640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (96238260).

81858640 is an abundant number, since it is smaller than the sum of its proper divisors (110617880).

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

81858640 is a wasteful number, since it uses less digits than its factorization.

81858640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11599 (or 11593 counting only the distinct ones).

The product of its (nonzero) digits is 61440, while the sum is 40.

The square root of 81858640 is about 9047.5764710778. The cubic root of 81858640 is about 434.1983562416.

The spelling of 81858640 in words is "eighty-one million, eight hundred fifty-eight thousand, six hundred forty".