644861 has 8 divisors (see below), whose sum is σ = 780480. Its totient is φ = 520128.

The previous prime is 644857. The next prime is 644863. The reversal of 644861 is 168446.

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

It is not a de Polignac number, because 644861 - 2² = 644857 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644863) 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, 2591 + ... + 2828.

It is an arithmetic number, because the mean of its divisors is an integer number (97560).

2⁶⁴⁴⁸⁶¹ is an apocalyptic number.

It is an amenable number.

644861 is a deficient number, since it is larger than the sum of its proper divisors (135619).

644861 is a wasteful number, since it uses less digits than its factorization.

644861 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5443.

The product of its digits is 4608, while the sum is 29.

The square root of 644861 is about 803.0323779276. The cubic root of 644861 is about 86.3950189315.

The spelling of 644861 in words is "six hundred forty-four thousand, eight hundred sixty-one".