81691912544 has 48 divisors (see below), whose sum is σ = 175764012480. Its totient is φ = 37066642560.

The previous prime is 81691912469. The next prime is 81691912661. The reversal of 81691912544 is 44521919618.

It is a happy number.

It is a junction number, because it is equal to n+sod(n) for n = 81691912492 and 81691912501.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 7934 + ... + 404285.

It is an arithmetic number, because the mean of its divisors is an integer number (3661750260).

Almost surely, 2^81691912544 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 81691912544, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (87882006240).

81691912544 is an abundant number, since it is smaller than the sum of its proper divisors (94072099936).

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

81691912544 is a wasteful number, since it uses less digits than its factorization.

81691912544 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 412803 (or 412795 counting only the distinct ones).

The product of its digits is 622080, while the sum is 50.

The spelling of 81691912544 in words is "eighty-one billion, six hundred ninety-one million, nine hundred twelve thousand, five hundred forty-four".