644651 has 16 divisors (see below), whose sum is σ = 802560. Its totient is φ = 505440.

The previous prime is 644647. The next prime is 644653. The reversal of 644651 is 156446.

It is a happy number.

It is a cyclic number.

It is not a de Polignac number, because 644651 - 2² = 644647 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 644651.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 644651.

It is not an unprimeable number, because it can be changed into a prime (644653) 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 15 ways as a sum of consecutive naturals, for example, 4856 + ... + 4986.

It is an arithmetic number, because the mean of its divisors is an integer number (50160).

2⁶⁴⁴⁶⁵¹ is an apocalyptic number.

644651 is a deficient number, since it is larger than the sum of its proper divisors (157909).

644651 is a wasteful number, since it uses less digits than its factorization.

644651 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 194.

The product of its digits is 2880, while the sum is 26.

The square root of 644651 is about 802.9016129016. The cubic root of 644651 is about 86.3856396887.

The spelling of 644651 in words is "six hundred forty-four thousand, six hundred fifty-one".