It is a happy number.
665 is nontrivially palindromic in base 9 and base 11.
665 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.
It is a sphenic number, since it is the product of 3 distinct primes.
It is a cyclic number.
It is a magnanimous number.
665 is an undulating number in base 9.
665 is a nontrivial repdigit in base 11.
It is a plaindrome in base 11, base 14 and base 16.
It is a nialpdrome in base 10 and base 11.
It is a zygodrome in base 11.
It is an amenable number.
665 is a wasteful number, since it uses less digits than its factorization.
665 is an odious number, because the sum of its binary digits is odd.
The sum of its prime factors is 31.
The square root of 665 is about 25.7875939165. The cubic root of 665 is about 8.7285187352.
Subtracting from 665 its reverse (566), we obtain a palindrome (99).