81221050728 has 64 divisors (see below), whose sum is σ = 226550332800. Its totient is φ = 26961327360.

The previous prime is 81221050711. The next prime is 81221050777. The reversal of 81221050728 is 82705012218.

81221050728 is a `hidden beast` number, since 8 + 122 + 1 + 0 + 507 + 28 = 666.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a junction number, because it is equal to n+sod(n) for n = 81221050692 and 81221050701.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 728076 + ... + 832187.

It is an arithmetic number, because the mean of its divisors is an integer number (3539848950).

Almost surely, 2^81221050728 is an apocalyptic number.

It is an amenable number.

81221050728 is an abundant number, since it is smaller than the sum of its proper divisors (145329282072).

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

81221050728 is a wasteful number, since it uses less digits than its factorization.

81221050728 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1560519 (or 1560509 counting only the distinct ones).

The product of its (nonzero) digits is 17920, while the sum is 36.

The spelling of 81221050728 in words is "eighty-one billion, two hundred twenty-one million, fifty thousand, seven hundred twenty-eight".