81208468721 has 4 divisors (see below), whose sum is σ = 82320913572. Its totient is φ = 80096023872.

The previous prime is 81208468717. The next prime is 81208468729. The reversal of 81208468721 is 12786480218.

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

It can be written as a sum of positive squares in 2 ways, for example, as 19026064225 + 62182404496 = 137935^2 + 249364^2 .

It is a cyclic number.

It is not a de Polignac number, because 81208468721 - 2² = 81208468717 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (81208468729) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 556222316 + ... + 556222461.

It is an arithmetic number, because the mean of its divisors is an integer number (20580228393).

Almost surely, 2^81208468721 is an apocalyptic number.

It is an amenable number.

81208468721 is a deficient number, since it is larger than the sum of its proper divisors (1112444851).

81208468721 is a wasteful number, since it uses less digits than its factorization.

81208468721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1112444850.

The product of its (nonzero) digits is 344064, while the sum is 47.

The spelling of 81208468721 in words is "eighty-one billion, two hundred eight million, four hundred sixty-eight thousand, seven hundred twenty-one".