81644864 has 28 divisors (see below), whose sum is σ = 185159904. Its totient is φ = 34990464.

The previous prime is 81644861. The next prime is 81644887. The reversal of 81644864 is 46844618.

It is a tau number, because it is divible by the number of its divisors (28).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81644861) by changing a digit.

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, 90674 + ... + 91569.

Almost surely, 2^81644864 is an apocalyptic number.

It is an amenable number.

81644864 is an abundant number, since it is smaller than the sum of its proper divisors (103515040).

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

81644864 is a wasteful number, since it uses less digits than its factorization.

81644864 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 182262 (or 182252 counting only the distinct ones).

The product of its digits is 147456, while the sum is 41.

The square root of 81644864 is about 9035.7547554147. The cubic root of 81644864 is about 433.8200532431.

The spelling of 81644864 in words is "eighty-one million, six hundred forty-four thousand, eight hundred sixty-four".