66857881 has 4 divisors (see below), whose sum is σ = 66874932. Its totient is φ = 66840832.

The previous prime is 66857867. The next prime is 66857887. The reversal of 66857881 is 18875866.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 18875866 = 2 ⋅9437933.

It can be written as a sum of positive squares in 2 ways, for example, as 53056656 + 13801225 = 7284^2 + 3715^2 .

It is a cyclic number.

It is not a de Polignac number, because 66857881 - 2¹³ = 66849689 is a prime.

It is a super-2 number, since 2×66857881² = 8939952503620322, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (66857887) 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, 645 + ... + 11581.

It is an arithmetic number, because the mean of its divisors is an integer number (16718733).

Almost surely, 2^66857881 is an apocalyptic number.

It is an amenable number.

66857881 is a deficient number, since it is larger than the sum of its proper divisors (17051).

66857881 is a wasteful number, since it uses less digits than its factorization.

66857881 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 17050.

The product of its digits is 645120, while the sum is 49.

The square root of 66857881 is about 8176.6668637043. Note that the first 3 decimals coincide. The cubic root of 66857881 is about 405.8674310558.

The spelling of 66857881 in words is "sixty-six million, eight hundred fifty-seven thousand, eight hundred eighty-one".