81816068640 has 96 divisors (see below), whose sum is σ = 272880679680. Its totient is φ = 20534226944.

The previous prime is 81816068627. The next prime is 81816068641. The reversal of 81816068640 is 4686061818.

It is a tau number, because it is divible by the number of its divisors (96).

It is a Harshad number since it is a multiple of its sum of digits (48).

It is a self number, because there is not a number n which added to its sum of digits gives 81816068640.

It is not an unprimeable number, because it can be changed into a prime (81816068641) by changing a digit.

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 15 ways as a sum of consecutive naturals, for example, 5005080 + ... + 5021399.

It is an arithmetic number, because the mean of its divisors is an integer number (2842507080).

Almost surely, 2^81816068640 is an apocalyptic number.

81816068640 is a gapful number since it is divisible by the number (80) formed by its first and last digit.

It is an amenable number.

81816068640 is an abundant number, since it is smaller than the sum of its proper divisors (191064611040).

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

81816068640 is a wasteful number, since it uses less digits than its factorization.

81816068640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10026514 (or 10026506 counting only the distinct ones).

The product of its (nonzero) digits is 442368, while the sum is 48.

The spelling of 81816068640 in words is "eighty-one billion, eight hundred sixteen million, sixty-eight thousand, six hundred forty".