81947418 has 64 divisors (see below), whose sum is σ = 199280640. Its totient is φ = 21943872.

The previous prime is 81947389. The next prime is 81947423. The reversal of 81947418 is 81474918.

It is a Harshad number since it is a multiple of its sum of digits (42).

It is a self number, because there is not a number n which added to its sum of digits gives 81947418.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 81696 + ... + 82692.

It is an arithmetic number, because the mean of its divisors is an integer number (3113760).

Almost surely, 2^81947418 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 81947418, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (99640320).

81947418 is an abundant number, since it is smaller than the sum of its proper divisors (117333222).

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

81947418 is a wasteful number, since it uses less digits than its factorization.

81947418 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1131.

The product of its digits is 64512, while the sum is 42.

The square root of 81947418 is about 9052.4813172964. The cubic root of 81947418 is about 434.3552663119.

The spelling of 81947418 in words is "eighty-one million, nine hundred forty-seven thousand, four hundred eighteen".