81999999999999 has 16 divisors (see below), whose sum is σ = 121493919824640. Its totient is φ = 54661069412280.

The previous prime is 81999999999997. The next prime is 82000000000003. The reversal of 81999999999999 is 99999999999918.

It is not a de Polignac number, because 81999999999999 - 2¹ = 81999999999997 is a prime.

It is a super-9 number, since 9×81999999999999⁹ (a number of 127 digits) contains 999999999 as substring.

81999999999999 is a modest number, since divided by 9999999 gives 8199999 as remainder.

It is a junction number, because it is equal to n+sod(n) for n = 81999999999891 and 81999999999900.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81999999999997) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (29) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 155210697 + ... + 155738114.

It is an arithmetic number, because the mean of its divisors is an integer number (7593369989040).

Almost surely, 2^{81999999999999} is an apocalyptic number.

81999999999999 is a deficient number, since it is larger than the sum of its proper divisors (39493919824641).

81999999999999 is a wasteful number, since it uses less digits than its factorization.

81999999999999 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 310958587 (or 310958581 counting only the distinct ones).

The product of its digits is 2259436291848, while the sum is 117.

The spelling of 81999999999999 in words is "eighty-one trillion, nine hundred ninety-nine billion, nine hundred ninety-nine million, nine hundred ninety-nine thousand, nine hundred ninety-nine".