66406891 has 4 divisors (see below), whose sum is σ = 66565800. Its totient is φ = 66247984.

The previous prime is 66406883. The next prime is 66406961. The reversal of 66406891 is 19860466.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 19860466 = 2 ⋅9930233.

It is a cyclic number.

It is not a de Polignac number, because 66406891 - 2³ = 66406883 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (66406831) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 78826 + ... + 79663.

It is an arithmetic number, because the mean of its divisors is an integer number (16641450).

Almost surely, 2^66406891 is an apocalyptic number.

66406891 is a deficient number, since it is larger than the sum of its proper divisors (158909).

66406891 is a wasteful number, since it uses less digits than its factorization.

66406891 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 158908.

The product of its (nonzero) digits is 62208, while the sum is 40.

The square root of 66406891 is about 8149.0423363730. The cubic root of 66406891 is about 404.9527781147.

It can be divided in two parts, 6640 and 6891, that added together give a palindrome (13531).

The spelling of 66406891 in words is "sixty-six million, four hundred six thousand, eight hundred ninety-one".