81521175728 has 20 divisors (see below), whose sum is σ = 161620471848. Its totient is φ = 39812666880.

The previous prime is 81521175679. The next prime is 81521175739. The reversal of 81521175728 is 82757112518.

It is a Smith number, since the sum of its digits (47) coincides with the sum of the digits of its prime factors.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 59244353 + ... + 59245728.

Almost surely, 2^81521175728 is an apocalyptic number.

It is an amenable number.

81521175728 is a deficient number, since it is larger than the sum of its proper divisors (80099296120).

81521175728 is a wasteful number, since it uses less digits than its factorization.

81521175728 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 118490132 (or 118490126 counting only the distinct ones).

The product of its digits is 313600, while the sum is 47.

The spelling of 81521175728 in words is "eighty-one billion, five hundred twenty-one million, one hundred seventy-five thousand, seven hundred twenty-eight".