645809 has 4 divisors (see below), whose sum is σ = 649716. Its totient is φ = 641904.

The previous prime is 645803. The next prime is 645833. The reversal of 645809 is 908546.

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 485809 + 160000 = 697^2 + 400^2 .

It is a cyclic number.

It is not a de Polignac number, because 645809 - 2¹² = 641713 is a prime.

It is a Duffinian number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 645809.

It is not an unprimeable number, because it can be changed into a prime (645803) 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, 1694 + ... + 2039.

It is an arithmetic number, because the mean of its divisors is an integer number (162429).

2⁶⁴⁵⁸⁰⁹ is an apocalyptic number.

It is an amenable number.

645809 is a deficient number, since it is larger than the sum of its proper divisors (3907).

645809 is a wasteful number, since it uses less digits than its factorization.

645809 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3906.

The product of its (nonzero) digits is 8640, while the sum is 32.

The square root of 645809 is about 803.6224237787. The cubic root of 645809 is about 86.4373341882.

The spelling of 645809 in words is "six hundred forty-five thousand, eight hundred nine".