81857917 has 4 divisors (see below), whose sum is σ = 83402460. Its totient is φ = 80313376.

The previous prime is 81857899. The next prime is 81858013. The reversal of 81857917 is 71975818.

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 72488196 + 9369721 = 8514^2 + 3061^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81857917 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 (81857417) 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, 772192 + ... + 772297.

It is an arithmetic number, because the mean of its divisors is an integer number (20850615).

Almost surely, 2^81857917 is an apocalyptic number.

It is an amenable number.

81857917 is a deficient number, since it is larger than the sum of its proper divisors (1544543).

81857917 is a wasteful number, since it uses less digits than its factorization.

81857917 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1544542.

The product of its digits is 141120, while the sum is 46.

The square root of 81857917 is about 9047.5365155384. The cubic root of 81857917 is about 434.1970779146.

The spelling of 81857917 in words is "eighty-one million, eight hundred fifty-seven thousand, nine hundred seventeen".