81691920444 has 48 divisors (see below), whose sum is σ = 200761037568. Its totient is φ = 25803262848.

The previous prime is 81691920413. The next prime is 81691920469. The reversal of 81691920444 is 44402919618.

It is a junction number, because it is equal to n+sod(n) for n = 81691920393 and 81691920402.

It is a congruent 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 15 ways as a sum of consecutive naturals, for example, 1353577 + ... + 1412640.

It is an arithmetic number, because the mean of its divisors is an integer number (4182521616).

Almost surely, 2^81691920444 is an apocalyptic number.

It is an amenable number.

81691920444 is an abundant number, since it is smaller than the sum of its proper divisors (119069117124).

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

81691920444 is a wasteful number, since it uses less digits than its factorization.

81691920444 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2766354 (or 2766352 counting only the distinct ones).

The product of its (nonzero) digits is 497664, while the sum is 48.

The spelling of 81691920444 in words is "eighty-one billion, six hundred ninety-one million, nine hundred twenty thousand, four hundred forty-four".