665221391 has 8 divisors (see below), whose sum is σ = 679158000. Its totient is φ = 651336192.

The previous prime is 665221327. The next prime is 665221411. The reversal of 665221391 is 193122566.

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

It is a cyclic number.

It is not a de Polignac number, because 665221391 - 2⁶ = 665221327 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (665271391) 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 7 ways as a sum of consecutive naturals, for example, 13871 + ... + 39023.

It is an arithmetic number, because the mean of its divisors is an integer number (84894750).

Almost surely, 2^665221391 is an apocalyptic number.

665221391 is a deficient number, since it is larger than the sum of its proper divisors (13936609).

665221391 is a wasteful number, since it uses less digits than its factorization.

665221391 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 25705.

The product of its digits is 19440, while the sum is 35.

The square root of 665221391 is about 25791.8861466160. The cubic root of 665221391 is about 872.9487257033.

The spelling of 665221391 in words is "six hundred sixty-five million, two hundred twenty-one thousand, three hundred ninety-one".