81993388536 has 112 divisors (see below), whose sum is σ = 236731339800. Its totient is φ = 26592380352.

The previous prime is 81993388513. The next prime is 81993388537. The reversal of 81993388536 is 63588339918.

81993388536 is a `hidden beast` number, since 8 + 1 + 9 + 93 + 3 + 8 + 8 + 536 = 666.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81993388537) by changing a digit.

It is a polite number, since it can be written in 27 ways as a sum of consecutive naturals, for example, 25795 + ... + 405773.

Almost surely, 2^81993388536 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 81993388536, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (118365669900).

81993388536 is an abundant number, since it is smaller than the sum of its proper divisors (154737951264).

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

81993388536 is a wasteful number, since it uses less digits than its factorization.

81993388536 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 380040 (or 380021 counting only the distinct ones).

The product of its digits is 33592320, while the sum is 63.

The spelling of 81993388536 in words is "eighty-one billion, nine hundred ninety-three million, three hundred eighty-eight thousand, five hundred thirty-six".