81997172 has 12 divisors (see below), whose sum is σ = 143566500. Its totient is φ = 40978176.

The previous prime is 81997159. The next prime is 81997189. The reversal of 81997172 is 27179918.

It can be written as a sum of positive squares in 2 ways, for example, as 16613776 + 65383396 = 4076^2 + 8086^2 .

It is a congruent number.

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, 7268 + ... + 14724.

It is an arithmetic number, because the mean of its divisors is an integer number (11963875).

Almost surely, 2^81997172 is an apocalyptic number.

It is an amenable number.

81997172 is a deficient number, since it is larger than the sum of its proper divisors (61569328).

81997172 is a wasteful number, since it uses less digits than its factorization.

81997172 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10210 (or 10208 counting only the distinct ones).

The product of its digits is 63504, while the sum is 44.

The square root of 81997172 is about 9055.2289866132. The cubic root of 81997172 is about 434.4431541318.

The spelling of 81997172 in words is "eighty-one million, nine hundred ninety-seven thousand, one hundred seventy-two".