81643872 has 24 divisors (see below), whose sum is σ = 214315416. Its totient is φ = 27214592.

The previous prime is 81643853. The next prime is 81643897. The reversal of 81643872 is 27834618.

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

It is a self number, because there is not a number n which added to its sum of digits gives 81643872.

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 3 ways as a sum of consecutive naturals, for example, 425133 + ... + 425324.

It is an arithmetic number, because the mean of its divisors is an integer number (8929809).

Almost surely, 2^81643872 is an apocalyptic number.

It is an amenable number.

81643872 is an abundant number, since it is smaller than the sum of its proper divisors (132671544).

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

81643872 is a wasteful number, since it uses less digits than its factorization.

81643872 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 850470 (or 850462 counting only the distinct ones).

The product of its digits is 64512, while the sum is 39.

The square root of 81643872 is about 9035.6998622132. The cubic root of 81643872 is about 433.8182962384.

The spelling of 81643872 in words is "eighty-one million, six hundred forty-three thousand, eight hundred seventy-two".