665605 has 4 divisors (see below), whose sum is σ = 798732. Its totient is φ = 532480.

The previous prime is 665603. The next prime is 665617. The reversal of 665605 is 506566.

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

It can be written as a sum of positive squares in 2 ways, for example, as 494209 + 171396 = 703^2 + 414^2 .

It is not a de Polignac number, because 665605 - 2¹ = 665603 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 (665603) 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, 66556 + ... + 66565.

It is an arithmetic number, because the mean of its divisors is an integer number (199683).

2⁶⁶⁵⁶⁰⁵ is an apocalyptic number.

It is an amenable number.

665605 is a deficient number, since it is larger than the sum of its proper divisors (133127).

665605 is a wasteful number, since it uses less digits than its factorization.

665605 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 133126.

The product of its (nonzero) digits is 5400, while the sum is 28.

The square root of 665605 is about 815.8461864837. The cubic root of 665605 is about 87.3116492727.

It can be divided in two parts, 66 and 5605, that added together give a triangular number (5671 = T₁₀₆).

The spelling of 665605 in words is "six hundred sixty-five thousand, six hundred five".