81999999 has 16 divisors (see below), whose sum is σ = 122035200. Its totient is φ = 54417528.

The previous prime is 81999997. The next prime is 82000031. The reversal of 81999999 is 99999918.

It is not a de Polignac number, because 81999999 - 2¹ = 81999997 is a prime.

81999999 is a modest number, since divided by 9999 gives 8199 as remainder.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81999997) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 789 + ... + 12830.

It is an arithmetic number, because the mean of its divisors is an integer number (7627200).

Almost surely, 2^81999999 is an apocalyptic number.

81999999 is a deficient number, since it is larger than the sum of its proper divisors (40035201).

81999999 is a wasteful number, since it uses less digits than its factorization.

81999999 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 13851 (or 13845 counting only the distinct ones).

The product of its digits is 4251528, while the sum is 63.

The square root of 81999999 is about 9055.3850829217. The cubic root of 81999999 is about 434.4481468108.

The spelling of 81999999 in words is "eighty-one million, nine hundred ninety-nine thousand, nine hundred ninety-nine".