81991089734400 has 5184 divisors, whose sum is σ = 400262581555200. Its totient is φ = 16219865088000.

The previous prime is 81991089734387. The next prime is 81991089734443. The reversal of 81991089734400 is 443798019918.

81991089734400 is a `hidden beast` number, since 8 + 1 + 9 + 9 + 108 + 97 + 34 + 400 = 666.

It is a Harshad number since it is a multiple of its sum of digits (63).

It is an unprimeable number.

It is a polite number, since it can be written in 575 ways as a sum of consecutive naturals, for example, 210774009406 + ... + 210774009794.

Almost surely, 2^{81991089734400} is an apocalyptic number.

81991089734400 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 81991089734400, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (200131290777600).

81991089734400 is an abundant number, since it is smaller than the sum of its proper divisors (318271491820800).

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

81991089734400 is a wasteful number, since it uses less digits than its factorization.

81991089734400 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 553 (or 521 counting only the distinct ones).

The product of its (nonzero) digits is 15676416, while the sum is 63.

The spelling of 81991089734400 in words is "eighty-one trillion, nine hundred ninety-one billion, eighty-nine million, seven hundred thirty-four thousand, four hundred".