665989 has 4 divisors (see below), whose sum is σ = 668556. Its totient is φ = 663424.

The previous prime is 665983. The next prime is 665993. The reversal of 665989 is 989566.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 989566 = 2 ⋅494783.

It can be written as a sum of positive squares in 2 ways, for example, as 613089 + 52900 = 783^2 + 230^2 .

It is a cyclic number.

It is not a de Polignac number, because 665989 - 2³ = 665981 is a prime.

It is a Duffinian number.

665989 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (665981) 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, 844 + ... + 1429.

It is an arithmetic number, because the mean of its divisors is an integer number (167139).

2⁶⁶⁵⁹⁸⁹ is an apocalyptic number.

It is an amenable number.

665989 is a deficient number, since it is larger than the sum of its proper divisors (2567).

665989 is a wasteful number, since it uses less digits than its factorization.

665989 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2566.

The product of its digits is 116640, while the sum is 43.

The square root of 665989 is about 816.0814910289. The cubic root of 665989 is about 87.3284366205.

The spelling of 665989 in words is "six hundred sixty-five thousand, nine hundred eighty-nine".