664645 has 4 divisors (see below), whose sum is σ = 797580. Its totient is φ = 531712.

The previous prime is 664633. The next prime is 664661. The reversal of 664645 is 546466.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 546466 = 2 ⋅273233.

It can be written as a sum of positive squares in 2 ways, for example, as 370881 + 293764 = 609^2 + 542^2 .

It is a cyclic number.

It is not a de Polignac number, because 664645 - 2⁵ = 664613 is a prime.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 66460 + ... + 66469.

It is an arithmetic number, because the mean of its divisors is an integer number (199395).

2⁶⁶⁴⁶⁴⁵ is an apocalyptic number.

It is an amenable number.

664645 is a deficient number, since it is larger than the sum of its proper divisors (132935).

664645 is a wasteful number, since it uses less digits than its factorization.

664645 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 132934.

The product of its digits is 17280, while the sum is 31.

The square root of 664645 is about 815.2576279925. The cubic root of 664645 is about 87.2696526366.

The spelling of 664645 in words is "six hundred sixty-four thousand, six hundred forty-five".