81368582749 has 4 divisors (see below), whose sum is σ = 81369885564. Its totient is φ = 81367279936.

The previous prime is 81368582747. The next prime is 81368582777. The reversal of 81368582749 is 94728586318.

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 41255703225 + 40112879524 = 203115^2 + 200282^2 .

It is a cyclic number.

It is not a de Polignac number, because 81368582749 - 2¹ = 81368582747 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 (81368582747) 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, 552742 + ... + 684295.

It is an arithmetic number, because the mean of its divisors is an integer number (20342471391).

Almost surely, 2^81368582749 is an apocalyptic number.

It is an amenable number.

81368582749 is a deficient number, since it is larger than the sum of its proper divisors (1302815).

81368582749 is a wasteful number, since it uses less digits than its factorization.

81368582749 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1302814.

The product of its digits is 23224320, while the sum is 61.

The spelling of 81368582749 in words is "eighty-one billion, three hundred sixty-eight million, five hundred eighty-two thousand, seven hundred forty-nine".