81536640 has 64 divisors (see below), whose sum is σ = 259904160. Its totient is φ = 21742592.

The previous prime is 81536639. The next prime is 81536669. The reversal of 81536640 is 4663518.

It is a tau number, because it is divible by the number of its divisors (64).

It is a hoax number, since the sum of its digits (33) coincides with the sum of the digits of its distinct prime factors.

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, 19314 + ... + 23153.

Almost surely, 2^81536640 is an apocalyptic number.

81536640 is a gapful number since it is divisible by the number (80) formed by its first and last digit.

It is an amenable number.

81536640 is an abundant number, since it is smaller than the sum of its proper divisors (178367520).

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

81536640 is a wasteful number, since it uses less digits than its factorization.

81536640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 42489 (or 42477 counting only the distinct ones).

The product of its (nonzero) digits is 17280, while the sum is 33.

The square root of 81536640 is about 9029.7641165204. The cubic root of 81536640 is about 433.6282857144.

The spelling of 81536640 in words is "eighty-one million, five hundred thirty-six thousand, six hundred forty".