81987391922 has 18 divisors (see below), whose sum is σ = 128575175967. Its totient is φ = 39206907036.

The previous prime is 81987391907. The next prime is 81987391943. The reversal of 81987391922 is 22919378918.

It can be written as a sum of positive squares in only one way, i.e., 40993695961 + 40993695961 = 202469^2 + 202469^2 .

It is an ABA number since it can be written as A⋅B^A, here for A=2, B=202469.

It is a Duffinian number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 9309173 + ... + 9317975.

Almost surely, 2^81987391922 is an apocalyptic number.

81987391922 is a deficient number, since it is larger than the sum of its proper divisors (46587784045).

81987391922 is an frugal number, since it uses more digits than its factorization.

81987391922 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 17654 (or 8828 counting only the distinct ones).

The product of its digits is 3919104, while the sum is 59.

The spelling of 81987391922 in words is "eighty-one billion, nine hundred eighty-seven million, three hundred ninety-one thousand, nine hundred twenty-two".