665391 has 4 divisors (see below), whose sum is σ = 887192. Its totient is φ = 443592.

The previous prime is 665387. The next prime is 665419. The reversal of 665391 is 193566.

It is a happy number.

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

It is not a de Polignac number, because 665391 - 2² = 665387 is a prime.

It is a D-number.

It is a Duffinian number.

It is a plaindrome in base 14.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (665311) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 110896 + ... + 110901.

It is an arithmetic number, because the mean of its divisors is an integer number (221798).

2⁶⁶⁵³⁹¹ is an apocalyptic number.

665391 is a deficient number, since it is larger than the sum of its proper divisors (221801).

665391 is a wasteful number, since it uses less digits than its factorization.

665391 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 221800.

The product of its digits is 4860, while the sum is 30.

The square root of 665391 is about 815.7150237675. The cubic root of 665391 is about 87.3022910218.

The spelling of 665391 in words is "six hundred sixty-five thousand, three hundred ninety-one".