81946021731840 has 4480 divisors, whose sum is σ = 379504033615872. Its totient is φ = 16522763304960.

The previous prime is 81946021731731. The next prime is 81946021731853. The reversal of 81946021731840 is 4813712064918.

81946021731840 is a `hidden beast` number, since 8 + 1 + 9 + 4 + 602 + 17 + 3 + 18 + 4 + 0 = 666.

It is a tau number, because it is divible by the number of its divisors (4480).

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

It is a congruent number.

It is an unprimeable number.

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 447 ways as a sum of consecutive naturals, for example, 311581831549 + ... + 311581831811.

Almost surely, 2^{81946021731840} is an apocalyptic number.

81946021731840 is a gapful number since it is divisible by the number (80) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 81946021731840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (189752016807936).

81946021731840 is an abundant number, since it is smaller than the sum of its proper divisors (297558011884032).

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

81946021731840 is a wasteful number, since it uses less digits than its factorization.

81946021731840 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 412 (or 381 counting only the distinct ones).

The product of its (nonzero) digits is 2322432, while the sum is 54.

The spelling of 81946021731840 in words is "eighty-one trillion, nine hundred forty-six billion, twenty-one million, seven hundred thirty-one thousand, eight hundred forty".