81221553792 has 480 divisors, whose sum is σ = 261021451680. Its totient is φ = 25010270208.

The previous prime is 81221553779. The next prime is 81221553793. The reversal of 81221553792 is 29735512218.

81221553792 is a `hidden beast` number, since 8 + 1 + 2 + 2 + 1 + 553 + 7 + 92 = 666.

Its product of digits (302400) is a multiple of the sum of its prime divisors (160).

It is not an unprimeable number, because it can be changed into a prime (81221553793) by changing a digit.

It is a polite number, since it can be written in 59 ways as a sum of consecutive naturals, for example, 912601684 + ... + 912601772.

It is an arithmetic number, because the mean of its divisors is an integer number (543794691).

Almost surely, 2^81221553792 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 81221553792, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (130510725840).

81221553792 is an abundant number, since it is smaller than the sum of its proper divisors (179799897888).

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

81221553792 is an equidigital number, since it uses as much as digits as its factorization.

81221553792 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 270 (or 160 counting only the distinct ones).

The product of its digits is 302400, while the sum is 45.

The spelling of 81221553792 in words is "eighty-one billion, two hundred twenty-one million, five hundred fifty-three thousand, seven hundred ninety-two".