645665 has 8 divisors (see below), whose sum is σ = 779328. Its totient is φ = 513520.

The previous prime is 645661. The next prime is 645683. The reversal of 645665 is 566546.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 645665 - 2² = 645661 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 645665.

It is not an unprimeable number, because it can be changed into a prime (645661) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1070 + ... + 1560.

It is an arithmetic number, because the mean of its divisors is an integer number (97416).

2⁶⁴⁵⁶⁶⁵ is an apocalyptic number.

It is an amenable number.

645665 is a deficient number, since it is larger than the sum of its proper divisors (133663).

645665 is a wasteful number, since it uses less digits than its factorization.

645665 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 759.

The product of its digits is 21600, while the sum is 32.

The square root of 645665 is about 803.5328244695. The cubic root of 645665 is about 86.4309092228.

The spelling of 645665 in words is "six hundred forty-five thousand, six hundred sixty-five".