81551821897728 has 2816 divisors, whose sum is σ = 338228593920000. Its totient is φ = 19177565847552.

The previous prime is 81551821897613. The next prime is 81551821897753. The reversal of 81551821897728 is 82779812815518.

It is a happy number.

81551821897728 is a `hidden beast` number, since 8 + 1 + 5 + 518 + 2 + 1 + 89 + 7 + 7 + 28 = 666.

It is a Harshad number since it is a multiple of its sum of digits (72).

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 127 ways as a sum of consecutive naturals, for example, 4292201152503 + ... + 4292201152521.

Almost surely, 2^{81551821897728} 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 81551821897728, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (169114296960000).

81551821897728 is an abundant number, since it is smaller than the sum of its proper divisors (256676772022272).

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

81551821897728 is an frugal number, since it uses more digits than its factorization.

81551821897728 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 121 (or 61 counting only the distinct ones).

The product of its digits is 180633600, while the sum is 72.

The spelling of 81551821897728 in words is "eighty-one trillion, five hundred fifty-one billion, eight hundred twenty-one million, eight hundred ninety-seven thousand, seven hundred twenty-eight".