81920212591 has 4 divisors (see below), whose sum is σ = 93623100112. Its totient is φ = 70217325072.

The previous prime is 81920212553. The next prime is 81920212681. The reversal of 81920212591 is 19521202918.

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 81920212591 - 2⁷ = 81920212463 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81920212991) 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, 5851443750 + ... + 5851443763.

It is an arithmetic number, because the mean of its divisors is an integer number (23405775028).

Almost surely, 2^81920212591 is an apocalyptic number.

81920212591 is a deficient number, since it is larger than the sum of its proper divisors (11702887521).

81920212591 is a wasteful number, since it uses less digits than its factorization.

81920212591 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 11702887520.

The product of its (nonzero) digits is 25920, while the sum is 40.

The spelling of 81920212591 in words is "eighty-one billion, nine hundred twenty million, two hundred twelve thousand, five hundred ninety-one".