81820188728 has 8 divisors (see below), whose sum is σ = 153412853880. Its totient is φ = 40910094360.

The previous prime is 81820188691. The next prime is 81820188731. The reversal of 81820188728 is 82788102818.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (8).

It is a self number, because there is not a number n which added to its sum of digits gives 81820188728.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5113761788 + ... + 5113761803.

It is an arithmetic number, because the mean of its divisors is an integer number (19176606735).

Almost surely, 2^81820188728 is an apocalyptic number.

It is an amenable number.

81820188728 is a deficient number, since it is larger than the sum of its proper divisors (71592665152).

81820188728 is a wasteful number, since it uses less digits than its factorization.

81820188728 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10227523597 (or 10227523593 counting only the distinct ones).

The product of its (nonzero) digits is 917504, while the sum is 53.

The spelling of 81820188728 in words is "eighty-one billion, eight hundred twenty million, one hundred eighty-eight thousand, seven hundred twenty-eight".