81641791239840 has 480 divisors, whose sum is σ = 312734460487680. Its totient is φ = 19938196002816.

The previous prime is 81641791239823. The next prime is 81641791239907. The reversal of 81641791239840 is 4893219714618.

81641791239840 is a `hidden beast` number, since 8 + 1 + 6 + 417 + 9 + 123 + 98 + 4 + 0 = 666.

It is a tau number, because it is divible by the number of its divisors (480).

It is an unprimeable number.

It is a polite number, since it can be written in 79 ways as a sum of consecutive naturals, for example, 19489171 + ... + 23304749.

It is an arithmetic number, because the mean of its divisors is an integer number (651530126016).

Almost surely, 2^{81641791239840} is an apocalyptic number.

81641791239840 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 81641791239840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (156367230243840).

81641791239840 is an abundant number, since it is smaller than the sum of its proper divisors (231092669247840).

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

81641791239840 is a wasteful number, since it uses less digits than its factorization.

81641791239840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3815746 (or 3815729 counting only the distinct ones).

The product of its (nonzero) digits is 20901888, while the sum is 63.

The spelling of 81641791239840 in words is "eighty-one trillion, six hundred forty-one billion, seven hundred ninety-one million, two hundred thirty-nine thousand, eight hundred forty".