81999264 has 24 divisors (see below), whose sum is σ = 215248320. Its totient is φ = 27333056.

The previous prime is 81999263. The next prime is 81999271. The reversal of 81999264 is 46299918.

It is a tau number, because it is divible by the number of its divisors (24).

It is a Harshad number since it is a multiple of its sum of digits (48).

It is not an unprimeable number, because it can be changed into a prime (81999263) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 426984 + ... + 427175.

It is an arithmetic number, because the mean of its divisors is an integer number (8968680).

Almost surely, 2^81999264 is an apocalyptic number.

It is an amenable number.

81999264 is an abundant number, since it is smaller than the sum of its proper divisors (133249056).

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

81999264 is a wasteful number, since it uses less digits than its factorization.

81999264 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 854172 (or 854164 counting only the distinct ones).

The product of its digits is 279936, while the sum is 48.

The square root of 81999264 is about 9055.3444992446. The cubic root of 81999264 is about 434.4468487606.

The spelling of 81999264 in words is "eighty-one million, nine hundred ninety-nine thousand, two hundred sixty-four".