644561 has 8 divisors (see below), whose sum is σ = 672000. Its totient is φ = 617760.

The previous prime is 644557. The next prime is 644563. The reversal of 644561 is 165446.

It is a happy number.

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

It is a cyclic number.

It is not a de Polignac number, because 644561 - 2² = 644557 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 644561.

It is not an unprimeable number, because it can be changed into a prime (644563) 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 7 ways as a sum of consecutive naturals, for example, 3140 + ... + 3338.

It is an arithmetic number, because the mean of its divisors is an integer number (84000).

2⁶⁴⁴⁵⁶¹ is an apocalyptic number.

It is an amenable number.

644561 is a deficient number, since it is larger than the sum of its proper divisors (27439).

644561 is a wasteful number, since it uses less digits than its factorization.

644561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 319.

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

The square root of 644561 is about 802.8455642276. The cubic root of 644561 is about 86.3816193896.

The spelling of 644561 in words is "six hundred forty-four thousand, five hundred sixty-one".