81685338840 has 512 divisors, whose sum is σ = 328902912000. Its totient is φ = 17615812608.

The previous prime is 81685338829. The next prime is 81685338841. The reversal of 81685338840 is 4883358618.

81685338840 is a `hidden beast` number, since 8 + 1 + 68 + 533 + 8 + 8 + 40 = 666.

It is a super-2 number, since 2×81685338840² (a number of 23 digits) contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (54).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81685338841) 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 127 ways as a sum of consecutive naturals, for example, 39787254 + ... + 39789306.

It is an arithmetic number, because the mean of its divisors is an integer number (642388500).

Almost surely, 2^81685338840 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 81685338840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (164451456000).

81685338840 is an abundant number, since it is smaller than the sum of its proper divisors (247217573160).

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

81685338840 is a wasteful number, since it uses less digits than its factorization.

81685338840 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2376 (or 2366 counting only the distinct ones).

The product of its (nonzero) digits is 4423680, while the sum is 54.

The spelling of 81685338840 in words is "eighty-one billion, six hundred eighty-five million, three hundred thirty-eight thousand, eight hundred forty".