81999918 has 256 divisors, whose sum is σ = 257402880. Its totient is φ = 18662400.

The previous prime is 81999889. The next prime is 81999941.

81999918 is nontrivially palindromic in base 10.

It is a Harshad number since it is a multiple of its sum of digits (54).

It is a Curzon number.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 127 ways as a sum of consecutive naturals, for example, 1999978 + ... + 2000018.

It is an arithmetic number, because the mean of its divisors is an integer number (1005480).

Almost surely, 2^81999918 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 81999918, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (128701440).

81999918 is an abundant number, since it is smaller than the sum of its proper divisors (175402962).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

81999918 is a wasteful number, since it uses less digits than its factorization.

81999918 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 120 (or 114 counting only the distinct ones).

The product of its digits is 419904, while the sum is 54.

The square root of 81999918 is about 9055.3806104437. The cubic root of 81999918 is about 434.4480037608.

It can be divided in two parts, 81 and 999918, that added together give a palindrome (999999).

The spelling of 81999918 in words is "eighty-one million, nine hundred ninety-nine thousand, nine hundred eighteen".