81721535575680 has 2048 divisors, whose sum is σ = 396540748800000. Its totient is φ = 15674697400320.

The previous prime is 81721535575613. The next prime is 81721535575697. The reversal of 81721535575680 is 8657553512718.

81721535575680 is a `hidden beast` number, since 8 + 1 + 7 + 2 + 1 + 53 + 5 + 575 + 6 + 8 + 0 = 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 pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 255 ways as a sum of consecutive naturals, for example, 847518511 + ... + 847614929.

It is an arithmetic number, because the mean of its divisors is an integer number (193623412500).

Almost surely, 2^{81721535575680} is an apocalyptic number.

81721535575680 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 81721535575680, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (198270374400000).

81721535575680 is an abundant number, since it is smaller than the sum of its proper divisors (314819213224320).

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

81721535575680 is a wasteful number, since it uses less digits than its factorization.

81721535575680 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 96492 (or 96460 counting only the distinct ones).

The product of its (nonzero) digits is 70560000, while the sum is 63.

The spelling of 81721535575680 in words is "eighty-one trillion, seven hundred twenty-one billion, five hundred thirty-five million, five hundred seventy-five thousand, six hundred eighty".