81321857 has 4 divisors (see below), whose sum is σ = 81599700. Its totient is φ = 81044016.

The previous prime is 81321847. The next prime is 81321871. The reversal of 81321857 is 75812318.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 49014001 + 32307856 = 7001^2 + 5684^2 .

It is a cyclic number.

It is not a de Polignac number, because 81321857 - 2²² = 77127553 is a prime.

It is a super-2 number, since 2×81321857² = 13226488851856898, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81321817) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 138482 + ... + 139067.

It is an arithmetic number, because the mean of its divisors is an integer number (20399925).

Almost surely, 2^81321857 is an apocalyptic number.

It is an amenable number.

81321857 is a deficient number, since it is larger than the sum of its proper divisors (277843).

81321857 is a wasteful number, since it uses less digits than its factorization.

81321857 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 277842.

The product of its digits is 13440, while the sum is 35.

The square root of 81321857 is about 9017.8632169711. The cubic root of 81321857 is about 433.2471978040.

It can be divided in two parts, 813 and 21857, that multiplied together give a triangular number (17769741 = T₅₉₆₁).

The spelling of 81321857 in words is "eighty-one million, three hundred twenty-one thousand, eight hundred fifty-seven".