81718640639 has 4 divisors (see below), whose sum is σ = 81720776520. Its totient is φ = 81716504760.

The previous prime is 81718640623. The next prime is 81718640659. The reversal of 81718640639 is 93604681718.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 93604681718 = 2 ⋅46802340859.

It is a cyclic number.

It is not a de Polignac number, because 81718640639 - 2⁴ = 81718640623 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 (81718640659) 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, 1009484 + ... + 1087425.

It is an arithmetic number, because the mean of its divisors is an integer number (20430194130).

Almost surely, 2^81718640639 is an apocalyptic number.

81718640639 is a deficient number, since it is larger than the sum of its proper divisors (2135881).

81718640639 is a wasteful number, since it uses less digits than its factorization.

81718640639 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2135880.

The product of its (nonzero) digits is 1741824, while the sum is 53.

The spelling of 81718640639 in words is "eighty-one billion, seven hundred eighteen million, six hundred forty thousand, six hundred thirty-nine".