81999998 has 4 divisors (see below), whose sum is σ = 123000000. Its totient is φ = 40999998.

The previous prime is 81999997. The next prime is 82000031. The reversal of 81999998 is 89999918.

It is a semiprime because it is the product of two primes.

It is a self number, because there is not a number n which added to its sum of digits gives 81999998.

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 as a sum of consecutive naturals, namely, 20499998 + ... + 20500001.

It is an arithmetic number, because the mean of its divisors is an integer number (30750000).

Almost surely, 2^81999998 is an apocalyptic number.

81999998 is a deficient number, since it is larger than the sum of its proper divisors (41000002).

81999998 is a wasteful number, since it uses less digits than its factorization.

81999998 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 41000001.

The product of its digits is 3779136, while the sum is 62.

The square root of 81999998 is about 9055.3850277059. The cubic root of 81999998 is about 434.4481450448.

The spelling of 81999998 in words is "eighty-one million, nine hundred ninety-nine thousand, nine hundred ninety-eight".