81993739968 has 672 divisors, whose sum is σ = 297213649920. Its totient is φ = 22055362560.

The previous prime is 81993739963. The next prime is 81993739969. The reversal of 81993739968 is 86993739918.

It is a happy number.

81993739968 is a `hidden beast` number, since 8 + 199 + 373 + 9 + 9 + 68 = 666.

It is a tau number, because it is divible by the number of its divisors (672).

It is a Harshad number since it is a multiple of its sum of digits (72).

It is a nude number because it is divisible by every one of its digits.

It is a junction number, because it is equal to n+sod(n) for n = 81993739896 and 81993739905.

It is not an unprimeable number, because it can be changed into a prime (81993739963) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 95 ways as a sum of consecutive naturals, for example, 138269080 + ... + 138269672.

Almost surely, 2^81993739968 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 81993739968, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (148606824960).

81993739968 is an abundant number, since it is smaller than the sum of its proper divisors (215219909952).

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

81993739968 is a wasteful number, since it uses less digits than its factorization.

81993739968 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 722 (or 699 counting only the distinct ones).

The product of its digits is 158723712, while the sum is 72.

The spelling of 81993739968 in words is "eighty-one billion, nine hundred ninety-three million, seven hundred thirty-nine thousand, nine hundred sixty-eight".