81445587721 has 4 divisors (see below), whose sum is σ = 81508095232. Its totient is φ = 81383080212.

The previous prime is 81445587697. The next prime is 81445587749. The reversal of 81445587721 is 12778554418.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 81445587721 - 2²⁹ = 80908716809 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81445587761) 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, 31251801 + ... + 31254406.

It is an arithmetic number, because the mean of its divisors is an integer number (20377023808).

Almost surely, 2^81445587721 is an apocalyptic number.

It is an amenable number.

81445587721 is a deficient number, since it is larger than the sum of its proper divisors (62507511).

81445587721 is a wasteful number, since it uses less digits than its factorization.

81445587721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 62507510.

The product of its digits is 2508800, while the sum is 52.

The spelling of 81445587721 in words is "eighty-one billion, four hundred forty-five million, five hundred eighty-seven thousand, seven hundred twenty-one".