81857861 has 4 divisors (see below), whose sum is σ = 81881292. Its totient is φ = 81834432.

The previous prime is 81857857. The next prime is 81857869. The reversal of 81857861 is 16875818.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 16875818 = 2 ⋅8437909.

It can be written as a sum of positive squares in 2 ways, for example, as 10201636 + 71656225 = 3194^2 + 8465^2 .

It is a cyclic number.

It is not a de Polignac number, because 81857861 - 2² = 81857857 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81857869) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 5306 + ... + 13851.

It is an arithmetic number, because the mean of its divisors is an integer number (20470323).

Almost surely, 2^81857861 is an apocalyptic number.

It is an amenable number.

81857861 is a deficient number, since it is larger than the sum of its proper divisors (23431).

81857861 is a wasteful number, since it uses less digits than its factorization.

81857861 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 23430.

The product of its digits is 107520, while the sum is 44.

The square root of 81857861 is about 9047.5334207728. The cubic root of 81857861 is about 434.1969789014.

The spelling of 81857861 in words is "eighty-one million, eight hundred fifty-seven thousand, eight hundred sixty-one".