66640891 has 4 divisors (see below), whose sum is σ = 66665872. Its totient is φ = 66615912.

The previous prime is 66640883. The next prime is 66640943. The reversal of 66640891 is 19804666.

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

It is a cyclic number.

It is not a de Polignac number, because 66640891 - 2³ = 66640883 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (66640801) 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, 7935 + ... + 14008.

It is an arithmetic number, because the mean of its divisors is an integer number (16666468).

Almost surely, 2^66640891 is an apocalyptic number.

66640891 is a deficient number, since it is larger than the sum of its proper divisors (24981).

66640891 is a wasteful number, since it uses less digits than its factorization.

66640891 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 24980.

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

The square root of 66640891 is about 8163.3872259008. The cubic root of 66640891 is about 405.4278686982.

The spelling of 66640891 in words is "sixty-six million, six hundred forty thousand, eight hundred ninety-one".