81999904 has 48 divisors (see below), whose sum is σ = 188008128. Its totient is φ = 34474752.

The previous prime is 81999889. The next prime is 81999941. The reversal of 81999904 is 40999918.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 8419 + ... + 15325.

It is an arithmetic number, because the mean of its divisors is an integer number (3916836).

Almost surely, 2^81999904 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 81999904, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (94004064).

81999904 is an abundant number, since it is smaller than the sum of its proper divisors (106008224).

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

81999904 is a wasteful number, since it uses less digits than its factorization.

81999904 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6977 (or 6969 counting only the distinct ones).

The product of its (nonzero) digits is 209952, while the sum is 49.

The square root of 81999904 is about 9055.3798374226. The cubic root of 81999904 is about 434.4479790361.

The spelling of 81999904 in words is "eighty-one million, nine hundred ninety-nine thousand, nine hundred four".