81993904 has 20 divisors (see below), whose sum is σ = 164342160. Its totient is φ = 39583040.

The previous prime is 81993889. The next prime is 81993913. The reversal of 81993904 is 40939918.

It is a super-2 number, since 2×81993904² = 13446000586322432, which contains 22 as substring.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 87892 + ... + 88819.

It is an arithmetic number, because the mean of its divisors is an integer number (8217108).

Almost surely, 2^81993904 is an apocalyptic number.

It is an amenable number.

81993904 is an abundant number, since it is smaller than the sum of its proper divisors (82348256).

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

81993904 is a wasteful number, since it uses less digits than its factorization.

81993904 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 176748 (or 176742 counting only the distinct ones).

The product of its (nonzero) digits is 69984, while the sum is 43.

The square root of 81993904 is about 9055.0485365900. The cubic root of 81993904 is about 434.4373824730.

The spelling of 81993904 in words is "eighty-one million, nine hundred ninety-three thousand, nine hundred four".