66666391 has 4 divisors (see below), whose sum is σ = 72726984. Its totient is φ = 60605800.

The previous prime is 66666371. The next prime is 66666409. The reversal of 66666391 is 19366666.

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 66666391 - 2⁵ = 66666359 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (66666311) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3030280 + ... + 3030301.

It is an arithmetic number, because the mean of its divisors is an integer number (18181746).

Almost surely, 2^66666391 is an apocalyptic number.

66666391 is a deficient number, since it is larger than the sum of its proper divisors (6060593).

66666391 is a wasteful number, since it uses less digits than its factorization.

66666391 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6060592.

The product of its digits is 209952, while the sum is 43.

The square root of 66666391 is about 8164.9489281930. The cubic root of 66666391 is about 405.4795741507.

The spelling of 66666391 in words is "sixty-six million, six hundred sixty-six thousand, three hundred ninety-one".