81591840 has 384 divisors, whose sum is σ = 333123840. Its totient is φ = 18432000.

The previous prime is 81591827. The next prime is 81591869. The reversal of 81591840 is 4819518.

It is a Smith number, since the sum of its digits (36) coincides with the sum of the digits of its prime factors.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a junction number, because it is equal to n+sod(n) for n = 81591795 and 81591804.

It is an unprimeable number.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 807790 + ... + 807890.

It is an arithmetic number, because the mean of its divisors is an integer number (867510).

Almost surely, 2^81591840 is an apocalyptic number.

81591840 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 81591840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (166561920).

81591840 is an abundant number, since it is smaller than the sum of its proper divisors (251532000).

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

81591840 is a wasteful number, since it uses less digits than its factorization.

81591840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 153 (or 139 counting only the distinct ones).

The product of its (nonzero) digits is 11520, while the sum is 36.

The square root of 81591840 is about 9032.8201576252. The cubic root of 81591840 is about 433.7261185488.

It can be divided in two parts, 8159 and 1840, that added together give a palindrome (9999).

The spelling of 81591840 in words is "eighty-one million, five hundred ninety-one thousand, eight hundred forty".