81608736640 has 64 divisors (see below), whose sum is σ = 206572142160. Its totient is φ = 30723284992.

The previous prime is 81608736637. The next prime is 81608736667. The reversal of 81608736640 is 4663780618.

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

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 7 ways as a sum of consecutive naturals, for example, 3739522 + ... + 3761281.

Almost surely, 2^81608736640 is an apocalyptic number.

81608736640 is a gapful number since it is divisible by the number (80) formed by its first and last digit.

It is an amenable number.

81608736640 is an abundant number, since it is smaller than the sum of its proper divisors (124963405520).

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

81608736640 is a wasteful number, since it uses less digits than its factorization.

81608736640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7500839 (or 7500827 counting only the distinct ones).

The product of its (nonzero) digits is 1161216, while the sum is 49.

The spelling of 81608736640 in words is "eighty-one billion, six hundred eight million, seven hundred thirty-six thousand, six hundred forty".