81691920443 has 4 divisors (see below), whose sum is σ = 93362194800. Its totient is φ = 70021646088.

The previous prime is 81691920413. The next prime is 81691920469. The reversal of 81691920443 is 34402919618.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 81691920443 - 2³² = 77396953147 is a prime.

It is not an unprimeable number, because it can be changed into a prime (81691920413) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 5835137168 + ... + 5835137181.

It is an arithmetic number, because the mean of its divisors is an integer number (23340548700).

Almost surely, 2^81691920443 is an apocalyptic number.

81691920443 is a deficient number, since it is larger than the sum of its proper divisors (11670274357).

81691920443 is a wasteful number, since it uses less digits than its factorization.

81691920443 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11670274356.

The product of its (nonzero) digits is 373248, while the sum is 47.

The spelling of 81691920443 in words is "eighty-one billion, six hundred ninety-one million, nine hundred twenty thousand, four hundred forty-three".