81720317149 has 4 divisors (see below), whose sum is σ = 81753364636. Its totient is φ = 81687269664.

The previous prime is 81720317117. The next prime is 81720317171. The reversal of 81720317149 is 94171302718.

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 27062553049 + 54657764100 = 164507^2 + 233790^2 .

It is a cyclic number.

It is not a de Polignac number, because 81720317149 - 2⁵ = 81720317117 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 (81720311149) 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, 16520034 + ... + 16524979.

It is an arithmetic number, because the mean of its divisors is an integer number (20438341159).

Almost surely, 2^81720317149 is an apocalyptic number.

It is an amenable number.

81720317149 is a deficient number, since it is larger than the sum of its proper divisors (33047487).

81720317149 is a wasteful number, since it uses less digits than its factorization.

81720317149 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 33047486.

The product of its (nonzero) digits is 84672, while the sum is 43.

The spelling of 81720317149 in words is "eighty-one billion, seven hundred twenty million, three hundred seventeen thousand, one hundred forty-nine".