66666891 has 8 divisors (see below), whose sum is σ = 89073664. Its totient is φ = 44352360.

The previous prime is 66666881. The next prime is 66666913. The reversal of 66666891 is 19866666.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 66666891 - 2⁶ = 66666827 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 66666891.

It is not an unprimeable number, because it can be changed into a prime (66666841) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 21355 + ... + 24276.

It is an arithmetic number, because the mean of its divisors is an integer number (11134208).

Almost surely, 2^66666891 is an apocalyptic number.

66666891 is a deficient number, since it is larger than the sum of its proper divisors (22406773).

66666891 is a wasteful number, since it uses less digits than its factorization.

66666891 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 46121.

The product of its digits is 559872, while the sum is 48.

The square root of 66666891 is about 8164.9795468207. The cubic root of 66666891 is about 405.4805878513.

The spelling of 66666891 in words is "sixty-six million, six hundred sixty-six thousand, eight hundred ninety-one".